I'm not exactly sure what I should be looking for but...
My TV has a Digital Audio Output (Coaxial) and I'm looking for a device that has an input. I'm not sure where to look, what's good, or even how much things like this cost. My old amplifier doesn't have any thing like that so I assume I need something new.
Most newer AV receivers or surround systems will support digital audio; either coax or optical. If you want to stay with your current amplifier, there are converters, but I don't think you gain anything with that kind of setup.
Generally, it would be better to not use the audio out from the TV to your amp. Instead, go directly from the audio source (DVD player, cable box, etc) to the amp.