And just to double check, are you 100% sure the right aux switch you’re trying to program for H9B is the right tip? Maybe you’re programming Ring when it aught to be T+R.

Also, on H9A, whatever # you assign for TIP, RING, or T+R in [XMT CC] of MIDI system settings has to correspond to H9B’s [RCV.CTL] CC#.

For example, if on H9A’s [XMT CC] TIP is set to CC#90, then H9B’s [RCV.CTL] PSW should assigned to CC#90 as well for the Tip switch connected H9A to control the Hotswitch on H9B using this MIDI capability.