Dunno if the Panny has a Zone 2, and don't think you can bridge among the 5 channels. 2 channels at 100 watts each should be way ore than enough for 2 channel music. It's the first watt that counts the most. I use a 5 watt per channel tube amp and have never felt 5 weren't sufficient - except for big orchestral works which get a bit congested at very high volumes. 100 watts should open those M60s up like a rose.

Enjoy the Music. Trust your ears. Laugh at Folks Who Claim to Know it All.