OK, let's get the basics out of the way.
Cable from the SoftStep Expander MIDI Out to the PF MIDI In.
Match the PF MIDI channel to the SoftStep [System settings -> MIDI -> RCV CH].
Set the PitchFactor to receive [System settings -> MIDI -> OUTPUT -> THRU].
Now, set up the pitch shifter parameters.
[System settings -> MIDI -> RCV CTL -> KB2 for the Pitch A knob].
[System settings -> MIDI -> RCV CTL -> KB3 for the Pitch B knob].
You mentioned using SoftStep foot pressure controllers to facilitate the pitch bends. Your pressure switches will have to be sending a CC message between 0-99, or a MIDI pitchbend message. I'll use CC1 here for Pitch A, and CC2 for Pitch B under System settings -> MIDI -> RCV CTL. [KB2 < C1, and KB3 < C2]. If you tap the right switch a second time, LEARN will allow you to pick up the CC message from the SoftStep.
In that same system level, if you tap the left footswitch a second time, you can set the PitchFactor range limits that an incoming MIDI message [0-127 value] will sweep. You have to be fast here. For a whole step down: Tap the left switch, turn the Pitch A knob to UNISON. MIN VAL is displayed shortly thereafter. Tap the left switch again, turn the Pitch A knob to – 2nd. MAX VAL is displayed shortly thereafter. A cycle of three left footswitcxh taps should show you the minimum value, the maximum value, and back again to KB2 < C1.
Of course, you can set the "range limits" on the SoftStep transmitting side, and leave the PitchFactor parameters at "full range". You'll have to know / experiment with what CC values will result in an octave down, whole step up, etc. As an example, I put together a chart for the H910/949 algorithm here. One thing to note: The CC values are going to be the same for some of the PitchFactor's effects, and different for others. Some algorithms have a coarser pitch resolution; others much finer. MIDI CC value 0-127 is going to be distributed differently; depending on the number of parameter values in the 'target'.
The quality and characteristics of your pitch bends depend greatly on what PF effect that you select. If you just want to use a single pitch shifter, move the Pitch Mix to that side. You may want to run 100% wet on the Mix knob (for an authentic pitch bend). The PitchFlex algorithm is tailor-made for this kind of effect. If you use that, you might want to "bind" your SoftStep MIDI message to PDL (instead of CC1 < KB2 / CC2 < KB3). In fact, that's a cool trick for any of the algorithms. Program any combination of PF knobs to an expression pedal sweep, then control the entire 'crossfade' from an external MIDI message [System settings -> MIDI -> RCV CTL — PDL < C1].
Here's another thread with some related information. Let me know how all this works out for you. There are some advantages to sending a MIDI pitchbend message (like return-to-center), but that has it's own quirks in the PitchFactor. If you get into some of those deeper SoftStep options, I'm sure that you be able to pull off some amazing effects with the PitchFactor.