Nick, although YPAO's setting of the M60s large is "correct" from the standpoint of their low bass capability, I'd nevertheless suggest that you set YPAO to skip that setting and manually set all speakers small, with the sub setting LFE. Give the EP500 more of the bass to handle that it does best and less to the M60s so that they can play the higher frequencies a bit more cleanly.
If you get the RadioShack SPL meter, I'd definitely suggest the digital rather than the analog model, as it has more comprehensive measuring modes(e.g., a "Max" level measurement).
