I feel your pain, with the 1st generation Standard/Ultra. The AxeFxII, IIRC, allows you to bottom out the low freq at 100Hz, which is definitely a bit better for bass. If you want to get really low with your frequency sweep, then you may need to employ a filter or Para EQ block with a frequency assigned to a footpedal controller in addition to or instead of the wah. Try combinations of the Mix parameter, or try running in parallel.
There have been a small handful of bassists - and guitarists who play/record bass - who have requested that FAS make a couple adjustments such as this as well as tuner and/or pitch tracking that does bass frequencies better. I'm not ripping on FAS here, but it seems like they've got plenty on their plate and this kind of stuff is fairly back burner. I'm with you on this though, 100%.
