Anyone Using Bose 901 speakers In A Home Theater?

Well g nakamato it sounds like time to experiment.  40 plus years is a long time to spend with any speaker.  Even state of the art speakers are going to have deterioration issues, let alone mass market items.
  Are you still in a 4 channel set up?  Is your amp driving all 4 channels?  Is your TV in the system and if so, do you have a center channel to help with dialogue?
   Your ideas about power are somewhat antiquated.  The amount of power required is most dependent upon the efficiency of the speakers.
  McIntosh gear has a high resale value.  You may be able to sell that behemoth and be able to fund a decent 5.1 surround system, including an AVR, particularly 
if you buy on the used market.  Audiophiles constantly Buy and resell gear and you will be able to get relatively new equipment at knockdown prices.

Just searched that power amp.  Someone is listing one for over $5000.00
Again, selling that off would fund  a really great sounding 5.1 system, even without buying used equipment, and it would probably sound several times better than your current set up