I think that would be ok (AV stuff and plasma on a 20a).

Both of the subs can go on the same 15a breaker.

Its actually a good idea to keep the subs of the same run as the display, I know when watching a CRT, my sub was plugged into the same line as my CRT, and every time the sub went off I got lines on the screen.

So keeping the subs off of the display is a good idea.

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