Maximum volume on my 220pro...

[Soniclife]

I measured the difference between a 200 and 400, it was 2.5 or 3db on the remote, exactly as you would expect. I did this before comparing the sound on a home dem. If you don't account for the output difference the dem is compromised.

To the original poster, going dual mono will give you more headroom, and is great, so something to consider, money no object. But I also wouldn't have any fear of going over 0, just set it to what it sounds best to your ears and enjoy.