Mike,
How loud are you playing them right now? Do you have an SPL meter you can use to measure it? I saw in a previous post that you have a Pioneer VSX-1015, which does 150W into 8 Ohms. This should be sufficient to drive the M60s to a level of around 110dB, which is EXTREMELY loud. Remember that a doubling in amp power (300W/channel) would only result in a 3dB increase in volume.
I invite you to play around with
this SPL calculator. Use 93db as the efficieny of the speakers, and then plug in numbers to your heart's content.
