Deneke AD20? Only ouputs 20-bit, correct, not 24 bit and also 44.1 kHz.
This is incorrect. The AD-20 samples at 20 bits, but dithers it down to a 16 bit output. Your end result is a 16/44.1 recording. It would fit your needs, except for the 24-bit part. You would also need a cable with a female 1/8 > XLR to run the mics to the preamp. You could then run the AD-20 to the MicroTrack through the S/PDIF connection. Again, the recording would only be a 16/44.1 recording.
Sanjay is correct, you could run dpa > MT direct, but I believe that the MT only provides 30 volts of power to the mics. Is this correct and could the dpa handle this degree of power being sent to them?