Luke72,
I find your experience intriguing, I am not familiar with your amps. Perhaps some others can also verify your take that the 7.2's are considerable more difficult to drive, I can't speak on that as I have not owned them, yet. To my knowledge the woofer and coax are the same units but of course there is the additional midrange and very different crossovers. Do I understand that the difference you notice is very considerable? It would be my guess that the dynamics is related to damping factor of the amps, the 7.2 would probably require additional control to exhibit similar dynamics to the 6 but a significant difference is puzzling.
I know an individual who went from 6 to 7.2 with Krell 350MCX's and didn't have any issues with lack of power or dynamics. Of course it depends on your listening tastes but this individual prefers large dynamic classical passages as myself and thought the 7.2's were significantly more dramatic given the same gear.
Thiel may have experience with your amps and can suggest an alternative, the Pass Labs and Mcintosh are both reasonably priced alternatives for high power although not as articulate as the considerably higher priced amps out there.
You also mention a tube preamp which I have found certain tubes can significantly affect the soundstage, my experience was also as much as swapping amps.
