I have a similar room to yours and possibly even worse in that I have a high vaulted ceiling and large openings to the upstairs and downstairs hallways.
What worked great for me was buying a Lyngdorf DPA-1 digital preamp with RoomPerfect room correction. It is a high-end stereo unit with 4 analog inputs and 5 digital inputs.
In my room the bass had a broad peak of about 6dB at 125Hz and a roll off of deep bass below 45Hz even though the speakers are rated -3dB at 22Hz. I also had some high frequency reflections that were blurring the sound a bit and making the treble peaky.
I've got one Room Tune in one corner behind one speaker but that's it for acoustic treatments outside of a few sofas.
The DPA-1 turned this room into one of the best acoustic venues I've ever heard and took my system from being "pretty good" to being extraordinary. It fixed the bass rise and brought out more deep bass and then totally fixed all my high-frequency problems.
The sound of the Lyngdorf is smooth, grainless, fast, ultra-detailed and musically sweet & natural. I couldn't be happier. Best of all, I have many voicing options that allow me to subtly tailor the sound of a given recording for its best performance (at the push of a button while listening). To me, the Lyngdorf is an audiophiles dream.
Initially I was worried that I would still want to use a tube preamp in line with the Lyngdorf to "sweeten it up" a bit. But I found this totally unnecessary and simply run my transport into one of the Lyngdorf's digital inputs. And even my turntable sounds terrific, so it's a win-win.
I mean, you can play around with copious expensive room treatments from now until forever but I don't think you will get the kind of excellent results the Lyngdorf provides. And I don't think any passive room treatment will do anything to boost your low bass. Plus, the DPA-1 has a built-in electronic crossover, so you could even add subwoofers in the corners with full room correction and time alignment if you want to really rock your house.
This is the 21st Century, why not step into it.
