A couple months ago I bought a new DVD player just because I didn't know of these. We recently got sat cable (which has optical output) and my HT receiver only has one optical input and a coaxial input. My DVD player only had optical output, so I got another DVD player that has both optical & Coaxial output. It's not a total loss however as I am putting a HT in my bedroom.
There is another device at partsexpress & radio shack that converts optical to coaxial or vice versa (which actually would have been what I needed).