Connect Macbook Pro to DacMagic DAC

Toslink to mini-toslink, glass fiber, steel jacketing for protection, scroll to the middle of the webpage:
http://www.lifatec.com/toslink2.html
Van Den Hul also makes some great glass optical cables.
http://www.vandenhul.com/p_B42.aspx

"can't I get better sound using a mini-rca from the Mac's headphone jack and running it into the DAC's Toslink input?"

yes you will most likely get better sound.

Update:
Got myself a mini-stereo to Toslink cable and connected it to the headphone jack of my Macbook Pro.  Downloaded several 24/96 albums off of HDTracks.com including 'Hotel 'California' and 'Paper Airplane'.  Now we are talking!!!  So far I have downloaded two players on the Mac that will play FLAC files; Pure Music and Decibel.

Both play the FLAC files at 24/96 and both sound great.  Overall I like the Decibel software the best.  It's has a simpler interface, doesn't require iTunes, and I think that it sounds better.  And, it only costs $33.  Pure Music is a bit more expensive at $129... According to the Decibel website the developer is working on upgrading the player to include playlists and other organizational  features.

Nice...

I've been very happy with my Wireworld Supernova 6-mini. I use it to connect my Macbook Pro, running Pure Music Software, to a Bryston BDA-1 DAC.