I ultimately decided against getting the TSR-700. And to make things a little more complicated I decided to take the old receiver in to a service guy to get an estimate and see if it was worth salvaging. He says he didn't really hear a hum. In any event he said it is in great shape, maybe just needs to be cleaned up, connections tightened and a bit of soldering. He will run an in depth bench test to make sure there isn't anything else going on. Work would cost less than $100 -- he won't charge if for some reason it doesn't take care of the issue.
Seems foolish not to have that done, but then I'll need to decide if I should just use it to buy myself time while all of the new stuff finally makes its way to the market, bugs are worked out and there are reviews.