Apparently on many modern macs the 3.5mm headphone audio jack supports Mini Toslink.
How can I tell whether my mac supports it, whether it supports surround sound (4 speaker or better), and whether the microphone input acts as a mini toslink input?
I can not find a direct source to note when Apple started making audio output ports toslink enabled. But to answer your other questions:
Do the following:
Take a look at Mactracker. You can find the specs for your own Mac by clicking the "This Mac" item in the left-hand pane.
From a quick look:
On the audio output side, the 3.5-mm analog/optical combo jack was added in Mac mini models from Early 2006 and in iMac models from the iMac G5.
On the audio input side, 3.5-mm analog/optical combo jack was added in Mac mini models from Early 2006 and in iMac models from Mid 2006. A line-level microphone or optical digital audio equipment can be connected to this port as described in this Apple support page (for the Macbook Pro).
Since you didn't list a mac model, you can just pop your serial number of the mac into this URL and see if your model has TOSlink or "digital audio equipment" listed in the specifications.
While not specific to mini TOSLINK, Apple lists all their 192kHz-compatible models on their "Play high sample rate digital audio on Mac computers" article. (The wording makes it sound like some machines supporting 176.4kHz may not be listed, though.)