What I would do, is use the B3 as your preamp, and plug it directly into the Effects Return of your amp. You can still run a DI from the B3, and you get the advantage of having an on stage 'monitor' to hear yourself.
I'm running a similar set up, using a Line6 HD500x into the effects return of an Ashdown 300 combo. Sounds great to me, and I know that the amp is easily capable of handling the low end, where I was never that sure about an active PA speaker / FRFR setup being able to. Pretty sure they are, but I didn't have a big enough budget to get a 'decent' speaker. The Ashdown was not only affordable, but is fairly uncoloured (to my ears).