@tubeguy76 I am still trying to figure out Ralph's paper on the issue, and other sources - I am happy to stand corrected.
When I bought my EL34 push-pull Class A tube amp from the bloke who made it he specifically asked what ohms my speakers were. I said rated at 8, with a brief dip to 6 somewhere.
That's fine, it won't stress anything.
Because he also included a 4 ohm tap in tediously hand-winding the transformers.
In the foreseeable future I may consult with him about making a tube pre-amp, and I'll be much more prepared to ask him difficult questions and actually discuss issues.