Agree with Gig Performer. It is very intuitive. Here's the approach I used:
- I used the global rackspace for my volume pedal only (exprs pedal

. I ended up mapping this to the output level in S-Gear
- I then created separate rackspaces for my s-gear presets
- each of these rackspaces used a unique control for exprs pedal A. e.g. My clean preset (#1) mapped the expression A to the vibrato speed and intensity. I can then dial a variable amount of vibrato for that patch
- i repeated this for the others (e.g. Leslie patch - mapped exp A to the MOD thing depth and rate
- I also put a compressor vst in front of some of the cleaner patch rackspaces
- the wiring path I used was Audio Interface > compressor > S-gear VST3 > To Global Rackspace (My distorted patches don't use a compressor in front of S-Gear)
I used the "learn" capability by actually pressing the buttons on the FCB1010 but ended up just typing in values for the expression pedal limits as it was fasteer and more precise.
Bottom line - Gig performer is a way better solution than Mainstage imo. It is $180 vs $30 but Mainstage is a strange piece of kit.
In a surprising twist I ended up setting up my s-gear live rig using Ableton Live Lite 11. I already had a license for it and it was straightforward to map my s-gear presets to 7 channel striips and I used the 8th for the Ableton Tuner.