The amp switching will not work with MIDI, but there are custom adapters that will let you switch the Mark V 35 amp functions using the expression/control TRS ports. I have the same amp and can confirm that all footswitchable amp functions can be switched from the HX Effects, but I haven't tried it on the helix. My only gripe is that amp controls will take up a switch and can't be mapped along with other effect changes unless you're using snapshots. That was a big disappointment for me.
Here is the cable I'm using:
https://btpa.com/AS-MARKV3501-XX.html
