Hey guys. I just got a Line 6 HX effects pedal and channel switching is working with my Mesa Boogie Rectoverb 25.
Latest firmware 2.50
Guitar cable from exp1 line out to mesa boogie footswitch in
Global settings - set exp1 to exr amp and left set at tip1
Controller assignment to activate amp switching with footswitch 1.
So it's not a Helix but it does work with HX Effects.