The optical outputs on your Studio 192 are ADAT format only: 8 channels at 24bit 44.1KHz / 48KHz and 4 channels at 88.2KHz / 96KHz.
The SPDIF Output is the RCA connector on the back that uses a 75 Ohm SPDIF cable that you can connect to your surround speakers, however you will only hear audio in the Left and Right main as the Studio 192 does not send the encoded AC-3 / DTS signal that your surround sound speakers would decode.
If your surround system only has an optical input, then you would need to get a Coax to Optical Digital Format Converter to convert RCA SPDIF to Optical SPDIF to use with your surround speakers / receiver.
Note: Surround Sound AC-3 / DTS is a format unto itself that must be encoded using a plug-in from your mix, then it can be burned into a format that can be sent from a source file or disc (ie DVD / Blu-Ray disc, or video game or movie) that uses the AC-3/DTS signal for it's sound output, then the speaker system decoder / home receiver reads the signal and sends it to the different speaker outputs (i.e. 5.1).