I had a PSS-780 as a kid.
It had MIDI, drum pads under the keyboard, and a programmable drum machine, plus some (really) basic editing of the 2-op FM voices.
Apparently there was a shareware patch editor for Atari ST, but never tried it.
It even had a basic multitrack sequencer builtin.
UPDATE:
there’s a Ctrlr panel for editing patches on several PSS-x80 home keyboards.
http://ctrlr.martintarenskeen.nl/