Optical Cable

What you want is a glass (not plastic) Toslink cable. But I think they're more than $60.

I have tried several different quality toslink cables but never heard a difference between any of them. The only differences noticeable were in the construction of the various cables. My top favorites for construction are the Bettercables you mentioned and Wireworld's Supernova 5. The Bettercable has one of the nicest connectors of any cable I have owned, and it fits snugly in any component with a positive locking click.

How do you know it is glass and not plastic?

Dminches, I do no know them all. But here is a review of two of the on AA:

http://www.audioasylum.com/audio/general/messages/233584.html

Also, you can search Google for 'glass' and 'toslink'.

Since Toslink tranceivers (the little part on your equipment you plug the cable into) cost as little as four bucks, vs. ST glass optical tranceivers which cost at least $150, one determinant of whether or not you'll get better performance (than coax digital) with a good Toslink, is obviously what grade of tranceiver your component manufacturer has used in your equipment. Unfortunately, you have no control over that.