I was in the same boat a while back. I didn't want to be limited to only amps with HT bypass. I decided to try a selector from Amazon,(SOLUPEAK P2 2(1)-in-1(2)-Out Amp) which does a great job and allows me to choose which amp feeds the speakers. It's a simple device and I have noticed no loss in quality. No issues with the tube amp and Marantz AVR after a few years. I actually swap between tube and some vintage SS in that system because it's made it very easy. It's a simple device and you could always upgrade the wire inside if you wanted to.
