Is there such a think as a toslink to 3.5mm digital converter?

I am about to purchase my first HDTV, and I am going to use the HDMI input for my PS3, but I dont want to use the built in speakers on the TV. The only audio outputs are Toslink and og RCA cables. I have a very nice Boston Acoustics 5.1 surround sound system, but there is no way to plug these outputs into it, as it takes a 3.5mm digital cable. How do I convert the Toslink fiber optic to the 3.5mm digital?