SACD, in it's native form, is DSD, a one bit 2.8Mhz sample sample rate. However, DSD is not available via digital output except HDMI. In that case, it is sent to a DSD-capable processor (usually a surround pre/pro or receiver). To my knowledge, there are no standalone 2 channel DSD-capable DACs that accept this HDMI input from an SACD player. (Note: there are indeed a few DSD DACs but they get their DSD from proprietary files or pro workstations).
SACD players can also convert the DSD internally to PCM and send PCM out via HDMI. As has been stated in this Circle many many times SACD players convert to PCM at either 24//88.2k (Oppos, etc) or 24/176.4k (latest Sony's, early PS3, a couple Arcam models, etc). It is this conversion that allows my HDMI de-embedder solution to work (see review and discussion)
http://www.audiocircle.com/index.php?topic=82217.0So, there is no "theoretical digital output", it's via HDMI and it's either 1 bit/2.8Mhz or it's converted to PCM at 24/88.2k or 24/176.4k. No digital output available via coax or toslink.
