First thing we need to do is sort out what is what.
SPDIF = a standard format for sending digital signals
TOSLINK = an optical connector invented by Toshiba, almost an industry standard now on opticalcables
SP/DIF can be thought of as a set of rules that keeps everything compatible. So if you have optical cable or digital coax they can both use SPDIF, it is kind of like a digital pipeline between electronics regardless of the connenting cable. Then through this digital pipeline we can send many different digital signals -- PCM, DTS, dolby digital, etc.. A stereo pair is usually sent as PCM. (Pulse Code Modulation)
SO you have a digital out on your docking station, is it Coax with a RCA connector or something else?
If you have a digital out via coax with RCA, it is very simple to convert to optical with TOSLINK connector.
Here is an example of these converters.
And finally a USB to optical unit that is easy, cheap, and high quality is the M-Audio Transit, can be had on eBay for $60-70, it would act as your soundcard and has both analogue and Optical digital output.(Digital out via TOSLINK and MINI TOSLKINK)