Optical Audio to Digital Audio Decoder

I'm looking to use the speakers (Logitech X-540) with my laptop with 5.1... but this is an analog system (has green/black/orange inputs), and Macbook Pros only output with optical through mini-TOSLink. What's the best (read cheapest) device for decoding the optical output to analog?

If this won't work, I'm probably willing to shell out a bit more cash (Z-5500 perhaps). If you have a digital 5.1 system recommendation ($350 or less), let me know.

Manual for X-540 speakers: http://logitech-en-amr.custhelp.com/cgi-bin/logitech_en_amr.cfg/php/enduser/fattach_get.php?p_sid=7*z8_Y1k&p_li=&p_accessibility=&p_redirect=&p_tbl=9&p_id=5524&p_created=1160578991&p_olh=0

 

I have the z-5500 speakers for a few years now. Love them.

Anyway, this may be what you need.

http://www.hdtvsupply.com/optical-to-6-channel.html

 

rolleyes $250!! Holy hell... Might as well go for Z-5500s.

Perhaps an alternative method like an external sound card? Is there anything out there like the old Griffin Firewave?