Dentdog,
From what I have been able to find out about the MC 60 mono amp it does not have an AC noise capacitor installed on one of the AC 120V lines, that feed the power transformer of the amp. If it had I would have not recommended connecting the amps to a 60V 0V 60V (split phase) Balanced power system.
If it had the noise capacitor, even if you plugged both amps into the balanced power unit so the plug orientation would have been the same you still would have had a 60Vac potential to earth ground on one of the two hot AC power Lines, legs, that feed the power receptacle/s. Also depending on the preamp or any other piece of audio equipment connected together by wire ICs, that use a 3 wire plug using the safety equipment ground, there is a possibility enough leakage current would pass through the AC noise capacitor to chassis and cause the GFCI (Ground Fault Interrupter) on the balanced power unit to trip open. Like I said though, it seems your MC 60 amps do not have a noise capacitor installed on the AC line.
I believe this is the wiring schematic diagram for your MC 60 amps.
http://www.drtube.com/schematics/mcintosh/mc60.gif
No on/off power switches on the amps?
This AC forum link may be of interest to you. I did not read through the entire thread, only page 1.
http://www.audiocircle.com/index.php?topic=37076.0
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