optical is pretty much the worst digital interface. There isn't a good "Y-cable" solution. However, if you google for "spdif splitter", there are several products that will split and re-transmit the optical cable signal. Optical cable is a 1-way digital signal, so there is no worry about hand-shaking or communication. Two items that seem to have good results:
- J-Tech Digital Premium Quality SPDIF TOSLINK Digital Optical Audio 1x3 Splitter
($21.98 from Amazon)
- Metra ethereal AS-1X3TSPLIT
($29.99 from Crutchfield)