I've always used my M80s with a sub because:

1. I had one, and
2. I figured it couldn't hurt.

However, my room isn't huge, I don't listen at high volumes, and, at least on paper, the -3dB points of the sub & M80s are virtually identical.

That said, my woofers are NOT the "high power" ones. So now to my question - how much (if any) bass will I be "giving up" if I run the M80s "naked?"

My opinion is worth exactly what you're paying for it!