Bob
I do have a HT 2channel combination, as is your case audio is far more important to me than HT.
I had at one time everything in the HTS including the cable signal and stayed that way for quite a long time.
And then went to dedicated lines, improvement. then amp straight to wall improvement, took out all video out of HTS same result improvement. Then plugged ev direct to wall except video that was put in a separate circuit the best so far. Next ev video will be on HTS.
Just sharing my findings, my AC is not that bad but adding the HTS was an improvement vs no treatment nor dedicated lines.
Just for kicks do you have the HTS directly on the floor or rack? If you want to try an easy tweak put it over cones or any vibration tweak you might have.
I did this trick to a friend's system while listening to a CD: paused the disk, put the cones under (hard floor no carpet) and his jaw dropped.
Luis