I would call a 20' x 20' room large. Square can cause standing wave problems, but openings on 3 sides helps that a lot. No real delineations apply for "large" or "small"; the 'how much power is enough' is an ongoing unknown. But swapping amps is a big deal; but reports are consistent that more is better, all else equal, which it never is . . . As you all know, Thiel speakers are low impedance, requiring lots of current. However, that low impedance is gracefully resistive, which minimizes the problems. Classé DR amps are true current source output stages, so they match Thiel very well. All that said, bridged /mono configuration is less friendly to low impedance loads than normal mode. So, it's a soup, and I suspect your soup tastes pretty good.
Additionally I am exploring bi-amping and believe that we can get better performance from those two amps via split normal mode than from bridged mono mode. Since most solid state amps can drive half the impedance in normal mode relative to bridged mono, and since Thiel loads are low impedance, my hypothesis, my experience in general and with the CS3 and house 3.5s suggests that (vertically) splitting a normal-mode amp between bass and upper registers delivers the best of all performance. You have two appropriate amps. In your shoes, I would explore vertical bi-amping rather than swapping those amps for bigger ones.
Beetlemania will soon test that hypothesis with his bi-ampable hot-rod 2.4s. Also, I will be outfitting my PPs, 2.2 and 3.6s for comparative experiments as time allows, since I have 4 channels of Classé DR9 in my rig.
