I'd be tempted to have a play with it before shelling out a few quid. Stick in a 486DX266 CPU.
Jam in a PC power supply connecting it up as follows:
Yellow wiring in the machine is +5v
Brown wiring is +12v
Orange wiring is -12v
Fit a 24v supply capable of supplying 4A
Blue wiring in the machine is 24v.
The DSP problem could be sorted by cleaning the edge connector or re-seating the EPROMs.
It's worth trying it to see what you get out of it for the price of an old CPU and power supply. You wouldn't need to connect a 24v supply to run it up on a bench.