B&W 804S + $2,000 used integrated

I've owned a lot of B&W's, altho not the 804's. They tend to like a lot of SS power; & I'd think either of your choices would be very good. Plinius could also be well worth checking out.

What's your budget? And new or used?

Well, I've narrowed it down to either a Musical Fidelity a5.5 or a Vincent SV-236 MKII.

Can those "in-the-know" please explain to me the basic differences in sound I should expect between the two?

Also, would these be compatible with the B&W 683's as well?

Both are excellent and well reviewed, the MF being a powerhouse and the Vincent having a tube preamp. One of the Marantz PM integrated units might be a good choice as well.

Both of these amps are excellent and I think you would be happy with either. The MF is going to have a little more control over the woofers and perhaps a little better detail retrieval, while the Vincent is going to have a little more tube bloom and warmth. Either one is going to be very good with the B&Ws, depends on your preference. I have only heard the MF with B&Ws in auditions, and it sounds great. I think the Vincent would be easier to listen to over the long run if you are at all adverse to solid state treble etch, while the MF is going to be stronger on rock and classical recordings that demand extreme dynamic swings. Hope that helps.

As for the 683's I think that they would be well matched to either of these amps, with similar caveats applying as given above. The 683's are not as defined or precise as the 804s (or as interesting looking in my book), but may provide some great enjoyment with these amps and associated sources. If you are looking for heirloom speakers that could serve you through this amp upgrade to several more, then the 804s, are your choice.

I sold B&W,Mac,Krell etc 96-2001 just before 804S came out and go back and listen all the time at shop.That Music Fidelity would be fine and so would Vincent.But why the 804S?Forget 683's unless your going to flip them sometime.For me the keepers (best value for dollar) were 805's and the 803N/S.803D's.802's and 801's weren't as great a value as 803.Could never get why folks would get 804.I would either save money on the 805's or spend $1500 more ($3.5K versus $5K) on 803's which were waaay better than 804's in depth,sound stage everything.That said me I would spend $3K on 803's and get a 200 wpc Int.But that's not your question.Both 805's and 804's did not have the nasty impedance swing of the lager speakers in 800 line and run nicely of 60 tubes and 100 better.The Vincent looks like a value and has power for 804 (and could probably handle 803 in smaller room if not driven to hard) but bear in mind B&W's are very easy speaker to match and warm to begin with so the benefit less from tubes than brands which do (they also handled Krell we sold really well.805/804sounded great with their 300i In at 150 wpc and had incredible bass.On some speakers like a Thiel Krell would make your ears bleed!).If your into vocal and acoustic mostly go Vincent if not go MF.Sounds like you haven't gotten speaker so go deep and find a used pair of 803S of recent vintage!
Cheers
Chazz