How's the bass response in your room now? Do you think you'd significantly benefit from 2 subs?

I have never heard M80's, but if I had the space I would use them instead of my in/on wall M22's. What about keep the M80's and add an EP800? That would be a great combo for 70% HT watching.

What is your current setup?
In/On Wall 500 w M2 Center Channel