The Yamahas are decent receivers and since you have it already, why not just use it in 2-ch mode or whatever?
The resale on your Yamaha receiver probably isn't that great (not dissing, just my opinion, and I have Yamaha stuff) and the TOTL vintage receivers aren't necessarily cheap. There's a fairly big vintage crowd that usually scoops them up unless you happen to stumble upon something they've not found yet. Besides, most of them will need varying amounts of reconditioning to perform up to their original level.
Just throwing some thoughts out there....
Just because there is a knob doesn't mean you should turn it.