If you listen to a lot of music, a dedicated CD player would be a big upgrade from a standard DVD player; I dont' know what you have. The other thing would be the amplifier in your receiver; these are the things typically compromised the most in integrated units.
My $450 HK 3470 stereo receiver (100Wpc), which I got new for $300, has more power than all other Harman Kardon surround amps, except for the top-of-the-line, $2000 unit, I believe. It also has pre-out/main in jacks so I can use it as a dedicated amp for front channels, when I get a surround receiver.
I just saw an Onkyo 100Wpc dedicated amp on Circuit City's website for $300, and Harman Kardon has some 4-channel amps. The main difference would be the dynamic range of the amp. If you're happy with your DS777 in terms of performance at high volumes, then don't worry about it.
-Cooper
