You will notice a huge improvement moving from a 150 bogus wpc AVR to the Parasound A23 that will give you an honest 125 wpc with 45 amps of current to back it up. Something the Denon does not even dare publish with its small power supply trying to drive 9 channels. Or are they up to something higher now?
The A23 will smoke the Denon when it comes to driving a pair of speakers period.
But lowrider makes a good point about an integrated amp. What are your trying to accomplish? Improve the sound quality of listening to music as you mentioned your old 2 channel receiver. If so, just adding an A23 won't help as your still held hostage to the "pure direct" preamp section in the AVR that is just an afterthought in terms of quality. The power amp may drive the speakers but its the preamp that gives the refinement, soundstage, detail, etc. Something AVR's care less about.
Look into adding a quality 2 channel integrated amp with an HT Bypass feature into your surround sound system and you'll be amazed.