I have one compact and only use for very low volume solo gigs/home practice. I find vocals distort at even a moderate volume. I do have a Tyros 2 so maybe that's part of the problem?
In short I'd never buy another one.
I can't get mine to distort, without turning the input WAY too high. Be sure and check all levels. I usually run the Compact control at noon, then control the volume from the keyboard or mixer. I can get REALLY loud without distortion.
If you can't, there may be something wrong with your unit. It would be worth a call to Bose. Their customer support is unsurpassed.
DonM