Affordable, rack-mount version of the Yamaha FM synths from the 80s, though a bit different to the popular DX7.
Single instruments have 8 note polyphony, and there are performance patches that combines up to 4 instruments
Program Change
Software versions you can use in DAWs and VSTs, etc.
Program Change messages select patches:
You can set how these messages are routed, so you can Program Change 64 could switch to D05, via Utility > Midi Control? > Edit P.Cng Tbl?
You can setup instruments in performance patches to respond to MIDI messages on different channels, this is the only way to access multiple sounds at once of a single unit. All the default ones seem to be set to just use channel 1 for everything.
So ultimately you will want to create your own performance patches with sets of sounds you like, that can be easily access through a DAW or MIDI controller.