There seems to be a big misconception here about FRFR. Basically, FRFR is a means of hearing your signal without any further influencing factors that will otherwise change your basses tone. Whereas traditional bass cabs tend to have their own prebaked sound that influences your tone, a FRFR amp/cab setup does not. If you want to emulate a speaker cabinet, then you have to do so - typically via modelling. Likewise, your pre is what is doing your tone shaping and the FRFR output phase has no further influence.