Relationship of amplifier sound to transformer quality?

I meant to say similar to paralleling two channels of a stereo amp or in this case a pair of mono amps. However just the PSUs paralled accomplishes the same thing.

They are in parallel which means combined together working simultaneously.

Actually, both PSU will not output exactly same voltages (e.g. one PSU output 55.1V and the other PSU output 54.9V), the one which output higher voltage will do all the work until the current demand from the load is high enough to make the voltage sag to the same voltage as the lower output voltage PSU, then the lower output voltage PSU will start supplying the current to meet the requirements.

I suppose voltage differences must be very slight. Will the power diodes prevent circulating current in the event the voltages don't match well? I suppose I will check to see how close they are before I proceed.

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.