I don't see why you would need MIDI.If you just want to get a stereo signal into your computer Midiman makes the DIO 24/48 it's got both Coax and Optical digital ins and outs and can be had for around $100.Cheers!
Midi (and the appropriate software) allows you move tracks back and forth between the PC and the 1680 in a synchronized way. So you can put several tracks into the PC and maintain sync between them.