You say that the 2nd box is fed from the original panel? Relocate the AC, or the audio rig, so as to be sourced from the first panel, in other words, completely rework the load distribution for better isolation.
Central AC Ruining MY System Sound
My system is connected on three dedicated lines.They are from a new breaker box fed from my original panel.It has five 20a breakers, three being used by the system,two left as spares.We had central air put in,which was installed when I wasn't present.They used the two spares doubled up.The net result,my sound is terrible.Images are shifted to one side,and sounds fuzzy.If I turn off the ac and furnace breakers,Everything sounds great.Is there a way to correct this.Can a separate line be brought in from the outside to a third panel box with just the ac on it.One electrician I spoke with says no.Also don't want and can't afford a power regenerating unit such as a PS/Monster etc.Would really like to hear from anyone who has had a similiar situation, and solved the problem.