Wade:
 
That might work in a similar way to the ABY switch, but you still have the same summing problem at the back end of the SF-2.  If the SF-2 is set in stereo mode so that the two input channels are separate, then the outputs are separate too.  Essentially that the SF-2 needs to be set up as a stereo in and mono out.
 
Bill, tgo

Bill, would this work?
 
Epic  >  AB splitter  >  chs 1 & 2 SF-2  >  chs 1 & 2 F-2B w/ mono out.