Your macbook should have a dual audio/toslink output. You need a mini jack toslink to toslink cable. Silflex glass works great for about $70. Confirm, but all Macs have this output.
Alternatively, you will have to buy a USB to RCA/P/Dif converter. They can be had for a few hundred bucks.
Alternatively, you will have to buy a USB to RCA/P/Dif converter. They can be had for a few hundred bucks.