I have indeed used the M9 for DB.
I'll preface all this by saying I like the Walkabout much better; it's richer, warmer, rounder...
The M9 is pretty bright by nature. If you're after a darker old school, gut strings "thump and disappear" early driving straight 8 jazz thing; you'll likely be frustrated by it.
On the other hand, if you like a brighter tone, with well represented string and finger noise (it won't create it, but, you'll hear it if it's there) it can work well. The extended and crisp treble does a nice job of letting you "hear the air" in a DB.
The huge low end of the M9 can be hard to contain. I prefer voice 2, but, it adds a lot of low end. The GEQ is helpful here, and, can be helpful with feedback problems.
The comp limiter works well, and is fairly invisible about it; it doesn't "breathe," or squash things.
It can sound pretty nice for DB, it's waaaaaaay more power than I can use with DB.
Is that helpful? I sure wouldn't buy one for DB without a return/audition policy in place.
Lastly, it's going to depend-a lot-on your bass, your strings, your pickup, your outboard pre if you use one, and what speaker/s you use, and, your playing style.
It seems to me, all those sort of variables make much larger diff with db, than with electric.
