@ChatsworthMike you might want to start a new thread about this. But are the crossovers from 1977? If so I would think that there is a possibility they are causing your problem.
Higher voltage caps are fine. Lower voltage no. The outside of those can type caps are covered with an insulator so them touching should be no problem. Curious are the ones you're replacing 85 or 105 degrees C rated? If they're 105 make sure your replacements are also.
Common Impedance Coupling. It is when power and signal ground currents share the same wire. Some of the power ground current develops a voltage that gets added to the signal input.
I just looked at the back of a R112SW. The power cord has no Ground? Is this true or is it an old picture and Klipsch has since modified? So how can this be a ground loop? Sounds more like CIC. Just get a good quality isolator and fughetaboutdit.
If you want the best quality isolator that money can buy it's simple: Go to Jensen Transformer and get an ISO MAX.
No Affiliation, other than I know their stuff is good.
http://www.jensen-transformers.com/product/sub-1rr/