Amp channel switching is a contact closure, not a MIDI message. The amp expects two points shorted together, and it has no idea what did the shorting.
Judahs units drive this from a relay output. On the Kedem it is the TRS MIDI/Relay port, and on the PLS 8 there is a dedicated relay out.
Three facts decide whether a given amp works:
Some amps switch on a closure to ground and some on a closure between two points that are not ground.
Some amps need a latching state held, and some respond to a momentary pulse.
A tip-and-ring pair can carry two channels on one cable, which is how a two-channel amp runs from one jack.
The amp’s own footswitch is the reference. If you know what it does, the relay can be set to match it.