Kodiak, I think ultimately, in order to enjoy "loud", you will need an amp capable of 1000 peak Watts per side. That will get you to 100+ dB per side at your 20 foot listening position.

At that point, you will also need new speakers. Your M60s will start compressing at around that level...maybe even before.

It's really important though to spend some time with what you have before making any changes. Get to know the system to understand what you may be missing. Admittedly it's hard to know unless you've heard it before. Even with a great system, it's only as good as the recording. With good recordings, you should be hearing a soundstage at least as wide as the speaker width, depth equal to the distance to your front wall and the vast majority of images on the stage. The degree to which those images are separated on the soundstage, and their definition, depends largely on the accuracy of the speakers. With more accurate speakers, it's like your ears put on eye glasses.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated