When you asked about subs I gave some suggestions as to what could be used, but don't take that as a recommendation either for or against using them.

The multi-sub approach is a strategy that smoothes the energy distribution below the Schroeder frequency in any room. Because of that, it is a useful improvement for any home hifi system.

On the other hand, I'm not sure I see the advantage unless used with mains that provide a uniform reverberent field.

Speakers like the three π, four π and π cornerhorns generate a wide pattern that provides spectral balance throughout the room. They cannot, however, do much about room modes. The best thing to do to make energy uniform in the modal region is to have a well damped room and/or use distributed sound sources below the Schroeder frequency. When that is done, the energy distribution is spectrally balanced through the entire audio band over a very wide listening area.

Most speakers work best on-axis, and are not designed for uniform coverage over a wide area. In this case, the best place to listen is on-axis with both speakers. Other positions may not be unpleasant, but they generally aren't flat either. That being the case, it might be overkill to add a couple extra subs to smooth the modal sound field throughout the room. It wouldn't be completely unwarranted, because it would probably smooth the sound at the on-axis point too. But the multi-sub approach is done for uniform coverage, not for a single spot.

The one π, two π and two π tower speakers are designed for on-axis listening. They don't sound too bad off-axis horizontally, but they don't provide constant directivity. I generally like to remain within about 20° horizontally and at the same height as the midwoofer, no higher than the tweeter and no lower than the bottom edge of the midwoofer. That's where the one π, two π and two π tower speakers sound best.

The two π towers generate nice deep bass. They don't really need the extension from adding subs. And they aren't designed to cover a wide area, so I don't think multi-subs make sense. I don't run them with my two π towers. To me, thet sound great, all by themselves.