I remember Alan saying something about this... Something like there's a 1, 2, or 3 db difference in sound but no change in linearity on or off axis. Can't find the post.

Meaning, basically according to Axiom's tests there is NO difference.

On a side note I find the grill on the EP500 sufficiently rigid enough and fit snug against the cabinet. It must be the dimensions of the M60 that makes the difference

Cheers, Jag