Modular with option slots for many configurations: 16 channel AD converter, 16 Channel DA converter, 8 channel AD/DA etc. Optional cards include FireWire, Pro Tools HD, Pro Tools Mix, AES, DSD, MDSD etc. Reference Sync card has 2 RCA analog out, 2 ch AES I/O, BNC "monitor" out (?), word clock I/O, RS-232. Front has headphone out and lots of settings. Note: Each FireWire card can do 8 ch analog I/O at up to 96kHz, or 4 ch I/O at up to 192k, or 8 ch in at 192k, or 8 ch out at 192k. To do 8 ch in and out at 192k (or 16 ch in one direction at 192k), two FireWire cards are required.