Seems like I could just use a stereo power amp and control the volume from the Receiver.
NO!!! The only thing worse than an AVR’s amps is its preamp section, and a good preamp is absolutely crucial to getting good sound. That’s why I recommended an integrated stereo amp because then you’re completely replacing the AVR for critical 2-channel listening. What I’d recommend is minimizing your expense on an AVR that has front L/R preouts and maximize $$$ toward a good integrated stereo amp. Here’s the AVR I’d buy because it’ll do everything you need for HT processing and powering your center/surround speakers…
What are your speakers, what amp/pre/AVR do you have now, and what improvements are you looking for and what sound characteristics are most important to you? With this info we can start talking about stereo integrated options that would be worth exploring further. And yes, you have the correct idea that you’d use the front L/R preouts from the AVR into the integrated stereo amp, and if the integrated has a HT bypass function you literally push one button to switch between HT and stereo, and when in stereo the AVR is completely out of the system, which is what you want. It’s a beautiful thing really, because you literally have the best of both worlds in one system. I did this for years until I finally got my own dedicated listening room, and it was a great way to go. Goodonya for putting in the effort to research this option, because it will serve you well!