alt Hacker Newsright, so a very specific case of playing FLAC via an external device, not on the system itself. Ok, that makes more sense. Still don't get what the issue is. Put the device in the correct mode and play from whatever digital input or playback (CD, DAT etc) the system already has.
Okay, if there's a button you have to hold to enable firmware update then it's more sensible.
Probably still wouldn't want to use digital audio input though. Although it's a perfect digital stream, it's been processed in analog-like ways before it gets to the device - such as filtering and volume changes. So you'd still want to use a modem protocol over it.