Is AT&T a Good digital cable connection ?

Every piece of literature I've read says that the coaxial connection is better sonically than the fiber optic. Sorry, I don't remember the reasons. My Madrigal manuals recommend (best to worst): xlr, bnc coaxial, rca coaxial, glass. High end stuff doesn't even offer glass.

I used Altis Altima optical until my system got good enough to let me hear, very clearly, the superiority of S/PDIF coaxial or AES/EBU. Mgl123's comment on the literature also squares with my experience. I've heard that the signal has to be converted twice, with optical, since it starts out, and must end up, electrical. I hope I have that right, but don't bet the farm on it. Anyway, I'd avoid optical.

There is a difference between Toslink optical and ATT/ST. The ATT/ST is reputed to be a high quality link and many older high end products offered it, at least as an option. Few do now, tho. Have not compared, but is reported to be way better than Toslink.

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).

Jayt- Not all glass fiber transceivers are created (or implemented) equal. With certain manufacturers, Goldmund being one of them, the AT&T input is simply amazing. On C-J DAC, it was not! Copper does provide more "tuning" ability because again, not all coax sounds the same. However, with the gear I'm running, glass is the way to go. Just my .02.