Relationship of amplifier sound to transformer quality?

Voltage differences is highly expected, that is the reason insert power diode in series to isolate both PSU.
It's perfectly normal one PSU supply current to the load all the time and the other PSU kick-in when higher current is required. That is how this configuration works.

That's perfect. Thank you.

That's perfect. Thank you.

As above.
Paralleling power supplies is a problem waiting to happen.

Duly noted. I hope not. In any case, I will discover how closely matched they are first. If they are more than a few mil.v apart I think I will leave them alone and acquire a big transformer to experiment with instead. The Meridian 105s are serious world class amps even now, 40 years later. But their elegant compact form factor renders them a bit lean in the bottom end which is what consensus was back then and I'm very interested to find out what they can do with no holds barred.