Hello,

Loading any Program from the Program list will send a PC message. Example: Load Program 10 on the H90 and it will send PC 10.

Connect the H90’s MIDI output to the amp’s MIDI input. On the H90, set Output Mode to Transmit in the MIDI menu, and you should also set PC offset to 1 so the numbers match up. You also need to make sure both devices are using the same MIDI channel.

https://cdn.eventideaudio.com/manuals/h90/1.7.5/content/system-menu/midi.html

Let me know if that works.