A radical solution would be to SELL the Adcom and use the funds to purchase a good plate amp from maybe....Parts Express or Madisound...(Do they sell such amps?) so you can either use speaker level or line level input and get enough juice to do the driver justice.
I have an ancient Carver Cube that I shelved for similar reasons, though the cube IS bridgeable.
Adding 3db to the sub roughly doubled (2x) the power required.
HT setup is beyond me......I know there are many options. Run the front speakers as 'large'=full range or not and so on.
If that is the amp I think, the 15 yr+ old Pass design, while sturdy, you are coming up against the age of some components...mainly caps, which will eventually begin to tell.