On one leg or two legs?

They should be on the same side or leg of the panel and try to keep any motor loads such as bathroom exhaust fans, refrigerators on the other leg or side. Motors have back emf and will backfeed into your electrical system causing noise, keep them as far way as possible.

Just a note.
I think you want to put something on the other side or leg to keep the load some what even. Your breaker from the main panel to the sub pabel my not trip correctly the way you have it. Maybe you should run a 120Vac feed only not 208/230vac to the sub panal.

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.