There are pictures of each connector
HERE.
A coax cable is basically an RCA connnection. The difference is that you need a 75 OHM cable. Any old RCA cable won't cut it.
Optical (TosLink) uses a fiber optic cable and LED lights to transfer digital data. There is virtually no difference in sound quality between coax and optical.
S/PDIF is not an actual connection. It stands for Sony/Phillips Digital Interface. It is a standard for transfering audio digitally.
Do you have the Audigy card already? If not I would recommend a different one if you want to do it digitally.
The problem with the Creative cards, and most other sound cards, is that they do not output 5.1 sound over the digital connection when playing games. They will only output 5.1 when playing something like a DVD. The reason for this is that sound from a game needs to be encoded into Dolby Digital on the fly. There is only one soundcard that I know of that will do this. The
Bluegeards HDA Digital X-Mystique. It has a DolbyDigital Live chip which encodes everything into Dolby Digital on the fly. That is the only way you will get 5.1 sound over the digital connection.
I believe the onboard sound on some Nforce2 boards also had DDLive but the new ones do not. M-Audio was also making a DDLive card but I can no longer find it.
EDIT: Just noticed you were in Canada. I found one Canadian vendor selling the Bluegears card.
HERE it is.