I’ve experimented with this concept over the years, using various main speakers as well as different rooms. Presently, I’m using Klipsch Klipschorns and up to 4 M&K V125 subs in a 13x26 room; previously, I used Apogee Acoustics Full Range speakers with the M&K subs in a 14x14 room. I use a mini-DSP 10x10HD with up to 4 subs to address room modes, then I use an Integra pre/pro for surround sound. I can also run the main speakers through a purely analog signal path without any processing or any assist from the subs; in this way, I can compare three different presentations: mains speakers powered by a purely analog signal path, mains plus subs, and mains plus subs with surround sound (Audyssey) processing. I measure the response using REW, and the resulting measurements look good. I have not taken measurements at a variety of listening positions, nor have I attempted to optimize for a variety of listening positions.
The miniDSP is needed to address several issues: the volume of the mains must be reduced because the subs are also active, and also, the volume and time delays of the subs must be adjusted. Physical placement of the subs is also a factor. I do tune the left and right sides independently, although some may argue whether that’s necessary in this frequency range.
The basic idea works great, and I’ve been very pleased. There are lots of articles on room tuning with multiple subs, although generally, the goal is to flatten the frequency response over a range of listening positions as might be needed for Home Theater. I will add that for a single listening position, Audyssey does a nice job dealing with this issue of room modes; however, Audyssey does add its own sonic “signature”, so it’s nice to be able to achieve this one goal without room correction systems that are adding other enhancements.
One last thought involves the issue of sounding accurate versus sounding good. Some musical selections truly do sound better to me with various types of processing. Sometimes, after repeated listening, I tire of this processing; sometimes, I add processing. I like being able to have options. Rarely, though, have I found that I like a musical selection without having first corrected for room modes.