What I specifically like about Mike's room is the size. A large room is just so much better in my opinion, because the size allows to greater reverberation without being unpleasant. Many people (and most rooms I've been in) have rooms which are more "normal-sized" rooms, living rooms etc type spaces that even when well designed and deadened sufficiently, are too dead. It's very difficult to get a small room to sound as good not just because bass modes are much more difficult to deal with, but because a small room demands a shorter RT60 time to sound "right," and this works nicely but you have a much smaller soundstage and less space for the music. This isn't just because the speakers are closer together and to you in absolute terms, but because the reverberation last longer and reflections are also more significantly delayed in a larger space. In a small room, almost all the reflections are very close to the direct sound, and that's bad, so you have to spend all your time wiping those out, and it's very difficult to maintain a diffuse soundfield while doing that. In the end, it can sound very very good, and extremely precise in imaging, but it doesn't have the size and depth and ambiance of a larger space.
A large room on it's own isn't always an advantage, because there are a lot of wealthy people with very large living rooms and big open lofty type locations with expensive stereos, and it just sounds hideous because they just stuck a stereo in a big bright reverberant space. And this sounds like a mess. I'd pick a small room that's very controlled over a big giant reverberant room any day.
But what makes Mike's space so unique is that it's so controlled and purpose built (VERY rare for large listening spaces as I mentioned) while being so large. It sounds like a "normal" room much smaller than it actually is when you're just in it, but it lends to the creation of music that's much larger than you could ever really get in a small space. It sound stupid to describe the music as being "more spacious" because of this, but that's what I would say anyway.
I think Mike's room would probably be great with multichannel. In my opinion, as rooms get smaller, the difference in RT60 time desired between 2-channel and multi-channel increases, and as rooms get larger that difference desired gets smaller. I think the best example of this is maybe the Seattle Cinerama, which is a very diffuse design (nested QRD diffusors all along the walls and wavy cieling diffusion along with larger wavy-wall diffusion design) which would never work in a very small HT space which should be much more dead. But in a larger space like Mike's, I think the need to be as dead for multichannel is less important, of course taken to an extreme with the large size of the Cinerama.
Definitely by far the favorite part of my visit to Mike's some time ago was the room. Although I haven't heard his new Von Schweikerts...
I don't know what kind of bass performance the room has, the speakers he had at the time didn't have much bass. But looking at the design of the room, there's tons of very thick soffit trapping all over the place, and because it's so large, I would expect bass performance to be extremely good and relatively uniform as you move around. Again, another huge advantage to such a large lofty room.