If you are noticing a difference in sound quality with the Carver and HK, if it is only at very high volume, then it is easily understood by the specifications, as that Carver puts out vastly more power per channel than the HK (375 watts RMS @ 8 ohms versus 80 watts RMS @ 8 ohms). If the problem is at all volumes, either your speakers are too difficult for the HK (what speakers are you using?), or there is likely something wrong with it.
You might be able to pick up some more 2 channel Carver power amps for not too much money, if you have the space for them. In fact, you might be able to get away with just one more channel of amplification, and use the HK just for surround channels, which typically are driven much less hard than the front.
Also, the Carver power amp is supposedly designed to emulate the performance of some tube amplifier Bob Carver made, though what, precisely, that involves is not well explained in the manual. I am sure that Carver would like you to believe that there is something unique about their amplifiers that make them better than other amplifiers, but I suggest resisting such ideas.
