Have you compared the M80s in pure direct to the M80s set to small with the subs?

2 things come to mind: your subs may not be optimally placed, your subs are not very capable in the 40-80 Hz region.

I know that with music, pipe organ excepted, I can't tell the difference between M80s alone vs M80s + ep350.
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Fred

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Blujays1: Spending Fred's money one bottle at a time, no two... Oh crap!