The amp isn't going to be your "go to" fix in this situation: you really need to find a set of speakers you like, and tune your room acoustics around them. I can promise you that $100 of home-made room acoustic treatment will have orders of magnitude more impact on your listening pleasure than changing similar spec'ed amps or receivers.
I'd buy a good Denon, Marantz, Yamaha, Rotel, Arcam, etc.that isn't top of the line and got the best deal on, and I'd be perfectly happy as long as I'd SET UP MY ROOM PROPERLY! Really-buy some floor rugs and put in some bookcases. I'm serious. If you feel the need to put more money into your system I'd buy a better sub before I'd buy a new receiver looking for warmth or brightness.