I have an OUTLAW 1050. I highly recommend that for stereo listening, you hook up your 2-channel sources via the "direct" inputs, thus bypassing all digital circuitry of the OUTLAW. This means, of course, that you won't have bass management capabilities while in direct mode, but your M80s should certainly be sufficient to carry the bass-load on all but the rarest recording (cannons in the 1812 overture, organ music, and the like).
That said, I can only imagine that you're either somehow sending the M80s a substantially rolled-off signal and somehow NOT sending your sub the difference, or maybe your sub just can't handle it (I'm not familiar with the model). But again, I HIGHLY recommend you run your M80s in direct mode for stereo sources, but if you insist upon incorporating the sub, then make sure the sub can handle it.
(And don't forget to unplug your OUTLAW before switching the impedance to 4 ohms!!!!!)
