@tubetime There seems to be a date code from early 1987. I suspect that the "PL" could stand for "programmable logic"; in 1991 I worked for its competitor Media Vision, which used 13 GAL16V8s on its first Pro AudioSpectrum.

Sound Blaster (and compatibles from Media Vision) added a microcontroller. I spent much time making a machine code disassembler for Intel-based Zilog parts, I think mostly Z86E20 and Z86C40. (Later I did the same for PlayStation's MIPS R3000A core.)