I have a dedicated hifi and a separate cinema setup. What I can say is that there is very little to choose between my current receiver and my amp in sound quality whereas that didn't use to be the case. The Marantz SR7010 has a max power consumption of 700w so I think we can assume it has a power supply to drive two channels to the full 120w per channel.
As others have said, an understanding of the specific dissatisfaction with the CM1 would be helpful, but I can't help feeling that the very small woofers would be its limitation for music as far as I was concerned.
Assuming the OP has to prioritise for budget reasons, I think it would be sensible to first audition the larger CMs, the 5s and even the 9s because they would pair well with the existing centre speaker (I know music is priority, but no harm keeping cinema capability). If they don't prove satisfactory at audition, then try other speakers and finally once the speakers are sorted and funds allow, add a stereo amp into the mix by running the FR and FL preamp outs of the AV reveiver through it for cinema and using the other inputs for music.
I've not been on here long enough to know the personalities well, but I have to say I agree with TrevC in that, in my opinion at least, the Marantz is unlikely to be the weak link, initially at least, and the poor bass response of the speakers a more likely culprit.