A multi-channel amp is perfectly capable of playing stereo music. The quality is the same, you just have to pay extra for 7.1 channels rather than 2. An amplifier doesn't know if it's playing a film or a film soundtrack on CD. The quality remains the same. It's a question of what suits you best.
I'd start with the Marantz Cinema 70s and work up the price range from there.
My experience has been different to this, I wanted to get rid of my amp and go back to just using the AVR as it's one less box, one less remote and my AVR has 2 zones so can play music in the living area and to garden speakers with one input.
It'd also mean one less streamer, not having to turn on 2 separate units, make sure they're both on the correct input etc. and my AVR plays much better with my Harmony Hub so having a separate amp is just a hassle and a 2nd thing using electricity.
My surround amp though seems to have "overun" with the bass on some tracks, it almost seems like it's been designed to give a more "rumbly" sound which may be better dynamics for effects in movies like explosions etc. .... If I swap the speakers back from the AVR to the amp it disappears.
Generally the bass and overall presentation with the amp is "tighter" and more controlled.
It's not an absolute day and night difference and I only recently bought a seperate amp having just used my AVR for stereo for many, many years but having now experiened it, despite the benefits of one unit I'm loathe to go back.
Previously I've bought relatively expensive AVR's believing a good one would be better for stereo, generally I'm not that fused with movies so going forward if ever my AVR needed replacing I'd but a much cheaper unit that just "does the job" for surround sound.
This of course may be down to my specific AVR but I'm not going to try changing it to find a new one's no different.
For me, the perfect system would be an amp that's brilliant for stereo, has HDMI Arc. a centre speaker for clear dialogue, left & right mains and a sub out as I'm not bothered about the rears but you'd still get a reasonable effect for movies..