I had the 990/7125 in the house before the 7500/7700 amps were available, and decided to upgrade to the 7500 when it was offered. And I am very glad I did. To my ears, the 7500 made a significant difference with my M80v2's: clearer mid-range (especially vocals) and tighter base. I'm not sure if it's just the additional power or some other improvements that were made to the new generation amps, but I am very happy I have the 7500 powering my M80v2's, VP150 and QS8's for side surrounds. I'm no expert as far as the technical issues with these new amps, but I feel that the M80v2's, even though they are very efficient and will "play" with lesser amounts of power, love the extra "juice." At 4 Ohms the 7500 is feeding them 300 WPC and they really shine. The 7125 does a good job but if you can afford it, I'd go for the 7500.
By the way, the 990 is no slouch either. Realizing of course that I was moving up from an older, first generation Dolby Digital Yamaha receiver at 85 WPC, the level of detail the 990 pulls out of both CD's and DVD's is great. I'm very pleased with the set-up, but remember I moved up from a basic budget system, slightly better than HTIB.
FYI, my room is 16' x 25' with a vaulted ceiling, and I'm using my old Yamaha and a pair of NHT Superones for the rear surrounds for the time being. The system fills the room nicely although I find myself listening to just the M80v2's in stereo for music much of the time if it's a well engineered CD. They sound that good.
Regards.
