On one leg or two legs?

Jea48,
I have been working alot in this weather. hevac ya know.
Houstonreef can put any load on the other side that he wants. I would put another rooms outlets on it myself or light. Make sure there are no dimmers or florecent lights. Do not use kitchen outlets & motor loads are bad. I do not think the projector would be good he will connect the ground and common through the cables. It does not matter the amps if the breaker only has a 120Vac going throu it may not trip correctly.

Houstonreef: Where are your amps to your other equipment?
Do you have tube equipment, phono stage, have you tried to change out some cables. move equipment around a little can stop hum in some instances. Your equipment mite not like each other. Are your power cords 90 deg to your interconnects or 6 inches away as this can cause RF interferance. All a/c create RF. You could just have a bad shield or bad cable.

Maril555,
The second paragraph in my reply to Jea48 is for you. I looked at the pictures of your system try moving things around a little and your speaker cable to your center speaker seems very close to your right amp. Speaker cables are not shielded and RF can be an issue.

Maril555. Do interconnect cables connect to both your surround sound processor and your 2 channel. The 2 preamps can have a differant potetial to ground and cause hum. Try disconnecting cables to the SSPre. I have this issue and have not figured out how to stop it other than keeping both systems seperate totally. I got it down to a hum I only here right at the speaker but to me it is too much.

Hevac1,
The two pole 60 amp breaker will trip just fine if there is an overload or short circuit on just the one pole of the breaker. It is designed to do so.

I assume the reason Maril555 paid to have the sub panel installed was to keep his audio branch circuits somewhat isolated from the loads in the main panel.

If you look at the pictures, Maril555 supplied, you will see he had plenty of room in the main panel for the 5 branch circuits.

Your post got me to look at the picture of the main panel again and that reminded me I was going to ask Maril555 why he didn't have the electrician move the two GFI breakers, across from the 2 pole 60 breaker, to another location in the panel.

Don't know where to begin, well:
I was hoping to find interference from my PC or cable, but no luck. I disconnected and unplugged PC, cable modem, wireless router, switched off all breakers, except the power amps- hum is still there.
Tried different speaker- still there
Tried different power cord- still there
Plugged the amp into a different outlet upstairs, separate from the dedicated panel, through the long extension cord- still there.
Hum, or buzz, is very constant in nature and nothing seems to change it. it does sound like a ground loop buzz to me, more, than anything else.
Again, L channel amp hums more, than the R channel with everything disconnected from it.
Hevac1, thanks for your ideas, but in lieu of the above statement, I don't think compatibility of the different components is the culprit.

Jea48,
I don't know why I didn't ask him to move GFI breakers (they are the ones with yellow markings on them?).
Where do you think they should be in the panel?

Did I mention how frustrating that is ?