The SRb has to be updated at the factory to SuperSlot compatible and then you have to have a SuperSlot db25 output connected to it. SRc is SuperSlot compatible, SRb needs an update to be.
That's my guess.
I buy from Sweetwater every now and then. They usually call, but I've never felt them pressuring me to buy more, just seems like slightly annoying customer service.
Having just done a show in the mountains of Montana last year, I'll say there is surprisingly more RF noise than you'd realize. Both sound units had random weird wireless issues.
I feel like range is an issue. I'm not sure if any of the firmware updates have helped range, but I haven't kept up up with updating, so maybe I should check. This week we were in a field, maybe 100 yards apart and my boom op was having drop outs.
I've read that sometimes the initial draw can trip the internal protection circuits in those batteries. Try not powering everything on at the same time and you should be fine.