One further note on bi amping. IMHO:
Bi amping has benefits. Without doubt, it certainly has theoretical benefits - an active x-over ahead of the power amps will generally produce better distortion and phase performance. Further, offloading deep bass to a subwoofer will likely increase any system's max clean SPL capability, but....
You're already bi amping this system when you add subwoofers. By bi amping the mains, you're effectively tri amping the system. While there may well be additional benefits to this approach, I'd agree that this is a low return on incremental spending.