improving music

Yes - much better

While an integrated amp or other component change may or may not help, could you please be a bit more detailed in your setup and what exactly you are unhappy with?

Oftentimes, system setup, speaker placement, crossover to sub, room conditions and other factors are the real culprits.

I agree with Erik. I am a huge HT bypass advocate.

If improving stereo music is the goal, get a quality 2 channel integrated with HT bypass and enjoy the best of both worlds in one system. Sadly, the 2 channel pre-amp sections found in most modern AVR's are just an afterthought by the manufacturer. I have yet to hear a "source direct" stereo mode in an AVR that I was impressed with. By getting an integrated amp, you'll be getting a much better pre-amp section. Also, try and choose a model that is higher in power and current than your Marantz and you'll be doing your home theater a favor too. You'll put more power into the mains while freeing up the AVR to handle the center and surrounds.

Again, the best of both worlds in one installation with just one push of a button!

Again, best of both worlds.