Thanks for the input, @everyone. @decooney , as far as the rectifier tube, it came with a Sovtek installed, I tried a Gold Lion for a short time, then a UK Amperex (which I am told is basically a Mullard that was branded Amperex) and recently when I was moving some stuff around to try out a high pass filter in my chain I put the Gold Lion back in. It gets quite warm, with all of them.
After posting this thread/question and evaluating everything, I am going to continue to find a way not to stack them--for both the possible EMI and the temperature that makes me a bit uncomfortable about the idea.