I had an Acoustic Research optical cable(cheapest one they have), I gave that to a friend that wanted an optical cable. Now I have a Tara Labs and I could not tell any difference between the two. I usually just use the dig. coax output. I can't put my finger on it but I prefer the sound of the coax.
P.S.- I think the AR cable was approx $20 at Best Buy. I don't know how much retail on the Tara Labs is but I got it new on Ebay for $15. If I had to guess I would say $40-$60.