Well, figuring that out was a challenge! But I got things set up on the BIAB end. Playing chord sequence C then D with "send chords to external device" sends this out on the IAC bus, as trapped by ReceiveMIDI:

channel 16 note-on C1 1
channel 16 note-on E1 1
channel 16 note-on G1 1
channel 16 note-off C1 64
channel 16 note-off E1 64
channel 16 note-off G1 64
channel 16 note-on D1 1
channel 16 note-on F#1 1
channel 16 note-on A1 1

I'd rather have single events to process than all the component notes of the chords, but that's a lot to ask. Maybe silent MIDI events, easily placed in the chord sheet, that could function as lighting cues?