Well.....if you like the way your Parasound A31 amp sounds you should stick with it and don't worry about hissing and it isn't audible from your listening position anyways....I wouldn't worry about it.
A better AC power line product will help lower the noise floor of your system. I would highly recommend either Audioquest Niagara series (1000, 5000, 7000) or any Shunyata Research power products. But your AC wall outlet needs to be grounded and I highly suggest to hire electrician to get a dedicated grounded line for your hifi setup.
It will make a world of a difference.
I myself use two Audioquest Niagara 7000 products in my dedicated home theater room since I have multiple high powered monoblock amps and a multi-channel amp in there. I have a pair of Classe Delta CAM-600 monoblock amps driving my main front speakers (B&W 800 D3); Classe CAM-300 monoblock amp (single) for my center speaker (B&W HTML1 D3); Classe CA-5300 five-channel amp for my surround speakers (B&W 804 D3 & 805 D3). I'm doing 7.1 setup. My AV preamp surround processor is Classe SSP 800. My only AV source is the Oppo UDP-205 4K UHD bluray player and a Sony 4K OLED TV (85"). My sub is a JL Audio Gotham.
All these gears but the sub are plugged into my two Audioquest Niagara 7000. The JL Audio Gotham sub is plugged directly to the wall outlet.
In my dedicated stereo setup in a separated dedicated listening room I have the Shunyata Research Hydra Typhon QR which consists of Hydra Triton & Hydra Typhon. I have two pairs of Dan D'Agostino Monentum M400 monoblock amps in bi-amp mode driving a pair of Magico M6 speakers. I use an Audio Research Reference 10 linestage analog stereo preamp. My digital front end consists of the DCS Vivldi full four stacks (Vivaldi master clock, Vivaldi upsampler, Vivaldi DAC, Vivaldi CD/SACD transport).
My analog front end rigs consist of the following : Kronos Pro turntable with a dedicated Kronos Pro stand, 12" Black Beauty tonearm, Air Tight PC-1 Supreme mc cartridge, class A linear PSU, Audio Research Reference 10 phonostage preamp.
All these gears are plugged into the Shunyata Research Triton & Typhon.
As for power amp choice, since you have B&W 804 D3 speakers I would highly recommend getting Classe amplifiers. Classe and B&W 800 series D3 speakers are meant to be paired together. They have perfect sonic synergy together. Especially the 800 series D3 these speakers were designed and tuned and voiced using Classe gears.
Either the Classe Sigma Amp5 / Sigma Amp2 amps or the higher end series Classe Delta series amps will sound phenomenal on your B&W 804 D3. The Delta series amplifiers are much more expensive than the entry level Sigma series amps but are better than the Sigma series amps and will be a noticeable improvements sonically from your Parasound A31. Try to find the nearest Classe dealer in your area to demo the amps. FYI, all Classe Delta series products were discontinued last year and can be had at discounts these days.
And these Classe Delta series amps exhibit astonishingly low noise floor. The noise floor is almost non-existent. Deadly quiet. The soundstage emerges from a very dark black background. Great amps. Especially the CAM-600 monoblock amps, like the ones I have in my dedicated home theater room. But these Classe CAM-600 monoblock amps will be way overkill for your B&W 804 D3. I think the Classe CA-2300 stereo amp will be perfect or even the much lower priced Classe Sigma series amps will be great choice for your speakers.
You mentioned that you are currently using a Denon receiver as your preamp processor and thinking to upgrade to the new Marantz AV8805. While the Marantz AV8805 processor would perform great for surrounds or home theater (movies) and will be a step up from your current Denon receiver but its stereo performance for stereo music playbacks or when used as a stereo preamp aren't on the same level of sonic qualities as high end dedicated stereo preamps. What are your priority? Do you use your setup for both stereo music and home theater (surround sound movies) or just mainly home theater? If you value stereo music playbacks I would highly recommend the Classe Sigma SSP preamp surround processor. This unit is optimized for stereo performance for music playbacks and its performance as a stereo preamp is superb and sounded more like a high end analog stereo preamp than an AV preamp processor. Its multi-channel of surround sound performances for movies is also excellent.
Preamp or preamp processor plays important role in achieving overall good sound for both your musical and movie sound effect reproductions.
The new Marantz AV8805 is great for home theater (surround sound movies) however.
A better AC power line product will help lower the noise floor of your system. I would highly recommend either Audioquest Niagara series (1000, 5000, 7000) or any Shunyata Research power products. But your AC wall outlet needs to be grounded and I highly suggest to hire electrician to get a dedicated grounded line for your hifi setup.
It will make a world of a difference.
I myself use two Audioquest Niagara 7000 products in my dedicated home theater room since I have multiple high powered monoblock amps and a multi-channel amp in there. I have a pair of Classe Delta CAM-600 monoblock amps driving my main front speakers (B&W 800 D3); Classe CAM-300 monoblock amp (single) for my center speaker (B&W HTML1 D3); Classe CA-5300 five-channel amp for my surround speakers (B&W 804 D3 & 805 D3). I'm doing 7.1 setup. My AV preamp surround processor is Classe SSP 800. My only AV source is the Oppo UDP-205 4K UHD bluray player and a Sony 4K OLED TV (85"). My sub is a JL Audio Gotham.
All these gears but the sub are plugged into my two Audioquest Niagara 7000. The JL Audio Gotham sub is plugged directly to the wall outlet.
In my dedicated stereo setup in a separated dedicated listening room I have the Shunyata Research Hydra Typhon QR which consists of Hydra Triton & Hydra Typhon. I have two pairs of Dan D'Agostino Monentum M400 monoblock amps in bi-amp mode driving a pair of Magico M6 speakers. I use an Audio Research Reference 10 linestage analog stereo preamp. My digital front end consists of the DCS Vivldi full four stacks (Vivaldi master clock, Vivaldi upsampler, Vivaldi DAC, Vivaldi CD/SACD transport).
My analog front end rigs consist of the following : Kronos Pro turntable with a dedicated Kronos Pro stand, 12" Black Beauty tonearm, Air Tight PC-1 Supreme mc cartridge, class A linear PSU, Audio Research Reference 10 phonostage preamp.
All these gears are plugged into the Shunyata Research Triton & Typhon.
As for power amp choice, since you have B&W 804 D3 speakers I would highly recommend getting Classe amplifiers. Classe and B&W 800 series D3 speakers are meant to be paired together. They have perfect sonic synergy together. Especially the 800 series D3 these speakers were designed and tuned and voiced using Classe gears.
Either the Classe Sigma Amp5 / Sigma Amp2 amps or the higher end series Classe Delta series amps will sound phenomenal on your B&W 804 D3. The Delta series amplifiers are much more expensive than the entry level Sigma series amps but are better than the Sigma series amps and will be a noticeable improvements sonically from your Parasound A31. Try to find the nearest Classe dealer in your area to demo the amps. FYI, all Classe Delta series products were discontinued last year and can be had at discounts these days.
And these Classe Delta series amps exhibit astonishingly low noise floor. The noise floor is almost non-existent. Deadly quiet. The soundstage emerges from a very dark black background. Great amps. Especially the CAM-600 monoblock amps, like the ones I have in my dedicated home theater room. But these Classe CAM-600 monoblock amps will be way overkill for your B&W 804 D3. I think the Classe CA-2300 stereo amp will be perfect or even the much lower priced Classe Sigma series amps will be great choice for your speakers.
You mentioned that you are currently using a Denon receiver as your preamp processor and thinking to upgrade to the new Marantz AV8805. While the Marantz AV8805 processor would perform great for surrounds or home theater (movies) and will be a step up from your current Denon receiver but its stereo performance for stereo music playbacks or when used as a stereo preamp aren't on the same level of sonic qualities as high end dedicated stereo preamps. What are your priority? Do you use your setup for both stereo music and home theater (surround sound movies) or just mainly home theater? If you value stereo music playbacks I would highly recommend the Classe Sigma SSP preamp surround processor. This unit is optimized for stereo performance for music playbacks and its performance as a stereo preamp is superb and sounded more like a high end analog stereo preamp than an AV preamp processor. Its multi-channel of surround sound performances for movies is also excellent.
Preamp or preamp processor plays important role in achieving overall good sound for both your musical and movie sound effect reproductions.
The new Marantz AV8805 is great for home theater (surround sound movies) however.