As long as I know this should not damage your MD unit or parallel port but USE AT YOUR OWN RISK. I accept no responsibility for any damage caused to your MiniDisc or computer.

The hardware interface is really simple, here's what you need:

Part
Quantity
6 wire shielded cable
1m
2 wire shielded cable
0.5m
Diode 1N4148
3
Male 3.5mm jack connector
2
Capacitor 1uF
2
74HC00 (or equivalent but CMOS)
1
CD4067 multiplexer (or equivalent)
1
25 pin male connector
1
small LED
1
small switch
1
470 ohm resistor
1
12K ohm resistor
2
resistors (see table for values)
1 each

Resistors values for MZ-R70:

Resistor name
Value
R1
2.5K
R2
6K
R3
100
R4
15K
R5
4K
R6
12.4K
R7
8K
R8
7K
R9
11K
R10
18.2K
1% precision resistors

schematics (download it)

cable (see how I did mine )

Last but not least a couple of photos (click to enlarge them):