If the M2 is distorting, try a 150Hz cut-off for it.

0.5dB gain resolution sometimes makes all the difference in establishing a more comfortable listening level.

Comparing gain levels across receivers makes sense only when the receivers and speakers both carry the same THX certification. Sources are also a factor.

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