I think there's at least one Pioneer with a DA15
serial interface, but
I have no idea if there's any sort of standard for them.
I think I used to have a Pioneer LDV1000
with a proprietory parallel interface
using a small Centronix-style connector.
I scrapped it because the power supply was blown,
and I got an RS232 interfaced one
that plays CAV and CLV with barcode scanner, etc.
I just touched the adapter box in my storage unit
that converted the parallel interface to RS232
and I have the manuals ... somewhere :-(