The 17881 from Aphex is an optional digital output card that adds digital connectivity to the 1788A microphone preamp. With the digital audio output module installed, three simultaneous digital outputs are available for each of the eight channels.
These are Alesis ADAT Lightpipe output (optical fiber interface,) Tascam TDIF on 25-pin D-sub and AES/EBU output on 15-pin D-sub connectors. Digital sync is derived from a selectable internal clock, or externally from the BNC clock input, which accepts Wordclock, Superclock or AES/EBU sync.