I can't tell you the number of times a sound engineer has tried to plug my pick-up into a high end direct box with unsatisfactory results. (The Countryman immediately comes to mind.) They often start troubleshooting without even considering impedance mismatch, which is the true culprit. You do have to worry about impedance mismatches with professional operators and gear!
Sorry to hear about your troubles, Vic. I checked your profile to see what kind of pickup you're using but didn't see one listed in your gear list.
I've seen Countryman DIs work great for upright bass pickups many times and have known bassists who carry one with them as their DI of choice. (I know there are different models.)
The OP has a Fishman Platinum Pro and, in the event of any issue with the "house" DI could say, "Hey, try this, it works fine." Problem solved. In that the Fishman has features useful to the player that the Countryman doesn't, I'd suggest that the OP offer it up preemptively.