I suggest you just try it and see what happens. The F2B has plenty of level and I doubt that you'd run into a tonal problem due to impedance issues. I've run mine into lots of different power amps, from McIntosh from the mid 60s to Crown and QSC from the last 5 years. No problems with any of them.
Impedance issues in this situation are not like dealing with impedance issues in amp to speaker situations. I do believe that this very issue has been addressed by Ron recently, although I'm not sure where the thread is.