I just stripped the setup down to bare bones and tried the following: Passive Yamaha BB1025x > Fliptop Boost > EWS Subtle Volume Control >Whirlwind IMP2 DI > Rolls PM50 for monitoring purposes.
The EWS is a passive volume knob that serves the purpose of stepping down whatever I'm sending to the DI before it goes to the Rolls, because the Rolls is notoriously unable to handle any sort of input from bass gear, or just about anything that isn't an actual microphone.
I was able to get the FTB up to noon easily, with barely stepping the EWS down at all. No distortion. I was able to max out the gain on the FTB without any distortion of any kind whatsoever, when compensated for by the EWS afterwards. At least no distortion from the FTB or the Rolls, running the FTB at 18v. The FTB gets ridiculously loud, and all by itself when maxed out I had to turn the EWS almost all of the way down to compensate and not fry the Rolls, but at no point was there distortion out of the FTB. Which leads me to believe that in my experience(s) thus far, it has never been the FTB overdriving, unless I'm hitting it with a hot pre or boost beforehand, and has just been everything after it that has been fried to high heaven by its raging output.