I have been strugglin with this too... Here's what I have, but I haven't gotten a chance to try it out:
SP Mics -> SP Battery box -> SP attenuator cable (basically a level control cable... $7 -> female 1/8" plug to 2 male XLR cable -> AD-20 -> NJB3 via optical...
The dude at SP said it would work. They also told me I would be able to run the mics into the mic in on my old MD, which was completely incorrect, so I am not sure what to believe.
At any rate, the attenuator cable from them was only $7, and it seems like it should work, in theory anyways.