TOS or Coax?

Firstly, if you try them you will hear a difference. Secondly, the Toslink is unsuitable for hifi. Thirdly, the difference is not the 1s and 0s that are transmitted, but the timing errors (ie. the gaps between the starts of the 1s and 0s are not uniform), called jitter. Toslink performs badly with respect to jitter. The effect of jitter is for the 1s and 0s to not arrive at uniform intervals at the DAC and this results in the sound coming out of the DAC having harmonic errors. Different forms of jitter result in different harmonic distortion. Some add grain, some soften perceived dynamics, some add ringing. Fourthly, do not believe that jitter can be eliminated by a jitter-reducer. Even with a jitter reducer in place, the sound improves when the transport or cable going into the jitter-reducer is improved. Fifthly, some people argue you should use a toslink connection into a jitter-reducer and a coax out. This is because the toslink breaks the earth connection between the transport and DAC (a good thing for jitter), and then the jitter-reducer supposedly fixes the jitter introduced by the toslink. From experience, I do not go along with this, because I still hear the detrimental effect of the toslink (which is usually to thin things out to the extent that the word anaemic springs to mind).

Big difference. Toslink is a very bandwidth limited interconnect. All other methods such as AT&T glass, Coax, and balanced are better. The problem is in the digital to light to digital convertion process. The converters in theater and low end CD/DVD players for TOS are very low grade, definitely not hi fi. Its not the same conversion hardware as AT&T glass despite the fact that they are both electrical to photon converters.