For example, on a monoblock, there's a left side and a right side, well for biasing anyway.
If I were to use 2 KT88 Sovtek's on the right bank, and 2 KT88 Tung sol's on the left bank, or even 6550's, if the bias sets correctly, is there a problem? Same goes for using front half and back half, where each bank would have a different tube.
Another related question, I've found that with small signal tubes anyway, buying a "matched" set really doesn't seem to make much difference, as some circuits might adjust accordingly, and, after some use, they're probably not matched anymore anyhow.
So is it really so important to install a "matched quad" in the M125? I know these are not small signal tubes. If I don't, so what?