The MarkII (black case) has a DDL which adds 5 parameters over the MarkI (grey case and faux LED graphics) wwhich just has chorus.

The Poly 800s work on summation of square waves (four octaves to switch in and out)instead of stored waveforms. It's surprising how many different sounds you can get that way. The Mark II's delay line is veery versatile and helps overcome the limits of 4-note polyphony (8 if you turn one source off). Neat 80s machine but would be fun to have a DW too.

Glad to be of help.mn