The biggest improvement will be changing the cd player, maybe check out Sony 555, Rega or Audio Research CD-1 as all three are nice payers. How much are you into 2 channel, as in most cases it's tuff to get the best of both worlds HT and 2 channel. If your happy with the speakers I would consider looking into changing the denon and replacing it with seperates if it's in the bugget. I'm 2 channel first then HT and could never have both in one room, tried it and hated it so I dedicate one room for 2 channel and one for HT.
Happy Listening!
Happy Listening!