I know how to switch Programs, Groups and Next Program via Midi – but how doI switch between A/B Machines via Midi.
There are various answers – one of them is to send a Sysex message that presses the key.
See SYSEXC_KEYPRESS in https://www.eventideaudio.com/downloader/1358 – the value for the A/B key is 0xFDFFFDFF.
You can also select between A and B by manipulating the MIDI channel when using Program Change messages. See UM p.126.