Integrated amp reccomendations

Hey all,
I want to upgrade my amplifier. I would like to stay in the integrated solid state world. I don't want the hassle or worrying about tubes, and a preamp-amp combo is probably out of my price range. My system is a Cambridge Audio Azur 640C CD player, an NAD C370 integrated amp, Sonus Faber Concerto Home speakers, and a REL Stadium III subwoofer. I use Cardas Cross Speaker cables, and Monster M550 Interconnects. OH! I also have a Musical FIdelity X10-V3 tube buffer between the CD player and integrated. I would like to buy a(new or used) integrated that will take a little of the hardness/edginess away from the sound. Give it a more fluid, life-like quality. It has to have enough power to run the Concerto's in a medium to large sized room with vaulted ceilings. The bass is handled by the REL, but I still want that midbass presence out of the Concertos. Lastly, I don't want to break the bank. I listen to everything from hard rock/metal to classical and acoustic music. Progressive rock/metal is my favorite, but of course, being progressive, it has a little of everything in it.

I know this is a tall order, but I need help.
My NAD always received good write-ups. Should I stick with it, or is there something reasonable in price that would be a real improvement?

Thanks in advance!