The M-Audio Firewire Audiophile is an external sound device that runs off Firewire. It has a built-in headphone amp for the 1/4″ headphone jack in front, a stereo RCA input, two stereo RCA outputs, one MIDI in and MIDI out, one S/PDIF coaxial in and out, and two Firewire jacks (the second one is for linking multiple Firewire devices in a row). If it is used with a 6-pin Firewire jack, it does not require the included AC adapter. The coaxial is nice for someone who wants to go DAC -> amp.