I was reading the thread on the guy that had the problems with his M80s and the Onkyo. He ordered the QSC and didn't think the M80s had enough bass. Anyway, I think for just music they are pretty impresive. I have some music that I think the sub adds some bass. But for the most part I can still enjoy the M80s without. But like you said, the sub really makes watching movies so much more fun. I have friends that are really amazed when there are some good scenes that make the room shake.
Will let you know what the outcome is. I know they are going to take care of it. Just need to match up the amp.