Best multichannel amp for quality stereo listening

We recently adopted a teenage boy and I'd like to adjust our living room system to better accommodate his movie watching tastes. I'm pretty happy with our current two channel system for music as well as movies (no action based movies until now) so, in this modification, want to keep this level of quality for music.

For a preamp I'm currently using a Peachtree Audio Nova which I will keep for music sources because of its large number and types of input choices. The current amp is a Peachtree 220 and the speakers are the Martin Logan Ethos' which I will keep as the front pair. The decision I need to make, then, is which multi-channel (5 is enough) processor / amp to buy. I still have an old B&K AVR307 that I used for surround listening years ago and which I could adapt but I would like some assurance that I will not lose any of the sound quality that I presently enjoy.

I assume there is a way to keep the current power amp in the system for 2 channel music listening but am having difficulty trying to envision volume control in a split system such as this would end up being.
I do not know if the Peachtree Nova has a HT Bypass input but that is the best way to integrate your two goals.

If it does, get a decent modern AVR with L/R line level outputs. That way the main speakers function as L/R for the HT operations and there is no complication with split VCs.
If you can make the B&K work, I would stick with it for 5.1 movie watching. Video inputs will be out of date, so it might require a couple remotes or a universal remote to get the audio modes to switch right when going between 2ch and movie watching modes. Spend the money on nice Martin Logan surround, sub and center speaker. You could also do a 4.1 system with no center. Start with a couple surround speakers and the B&K before you jump all-in.
You're right Kr4, but it doesn't have the by-pass so I'll have to pursue other options. Steuspeed, originally what I had in mind was to reinstall the B&K as a parallel system using a speaker switching panel allowing the fronts to be shared. This would allow me to maintain the two channel integrity of my current system but it further complicates its use for others that I share this setup with.

Coincidentally, I originally had an all ML surround setup including the center, rears and sub, with Odysseys as the fronts. Before I abandoned surround a few years ago, I had replaced the rears with in ceiling speakers and sold the ML center. I still have the sub in storage as well as a Focal Electra center speaker. I traded the Odysseys for the Ethos pair several months ago so I won't have to spend a lot of money on speakers to have, one way or another, a workable surround system again.

The easiest solution would be to ditch the Peachtree gear which I very much like, and purchase a quality HT processor/amp with the capability for high quality music reproduction. This takes me back to the original purpose of this post which is to identify the best surround equipment to satisfy that goal. I will still be using the Nova for music sources.