from the AD-20 (zefire inbox), you need to go S/PDIF out, which is the 1/8th jack on the side of the unit... the gmini 120 shoulw have come with a cable for the S/PDIF input, but with an RCA connector, so you need a mono 1/8th inch plug to RCA jack. these adaptors can be had for a couple of bucks at the radio shack...
although, as it stands today, the gmini 120 will not reliably record the S/PDIF signal. you'll probably get clicks and glitches throughout the recording. hopefully soon this will get fixed...