Is AT&T a Good digital cable connection ?

I have excellent experiences with the Translite ST-glass cable. This is not an ordinairy computer based cable, but dedicated to audio use. In my system it was slightly better than the MIT Reference XLR and the top Nirvana RCA and XLR.

With optical cable there is no electric connections between ground of the components.
The use of i/o gel (Aural Symphonics) is recommended.

Hope this helps.

Swampwalker is right, ST-glass is much much better than TosLink.
The implementation of AT&T sender and receiver-units are rather expensive....but the results are quite special (at least to my ears).