I could hardly find any modification possibilities for the PT-87, so I'm still looking for a circuit diagram. Up to now, I've only treated the device to a line out and a slight "drum distorter". Sadly, it doesn't have any Casio Chords accompaniment but the typical VL-1 /PT-30 sounds, instead. The drum sounds are very peculiar and sound very electronic.
It also has a ROM play module with lightning key function and a sort of evaluation game on board. The grotesque "rating"-sound and the ensuring "melody of success" (there are 4 different ones) can be heard in the audio example.