Upload & Sell: On
I'm gonna hope you already have liability insurance. If not, forget any suggestions I am about to offer. Get insurance, then come back and read this thread. Seriously, please don't even think about placing another strobe without it.
I don't think that gym looks that bad and I'm surprised bouncing didn't work. I bounce off a gym that has white ceilings, but there are large beams and HVAC units up in the rafters/beams that one would think would be a mess. I just bounce and let 'em do their thing. You might be surprised how far light will bounce around.
Here are a couple of videos that show a little of what I'm talking about.
I personally find the images from bounced strobes a little more appealing than direct. I shot direct in larger facilities where bouncing just isn't feasible. That's usually not HS gyms around here.
Finally, I think it would really help us help you if you could share some images and what exposure settings you were using. I'm surprised the B800s aren't working for you bounced.