The toslink glass fiber may have been stated to be better than toslink/coax, however toslink is still a compromised transfer mechanism. If anybody has googled around, the engineer from Lampizator did some scope tests and showed that the square waveforms from toslink weren't that square at all. The problem with toslink is not the glass medium, but it is that the LED light-emitting elements just cannot light up fast enough to produce that perfect square wave pulse that the Digital COAX cables can.
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USB vs COAX is a crapshoot - in some instances COAX is better, but there are some target devices which, apparently, perform better with USB. Obviously, COAX cannot transfer DSD.
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COAX s/pdif vs. AES/EBU. In theory, AES/EBU should be better because it's a balanced digital signal just like balanced XLR audio. However, I have read some discussion where COAX will perform better because of proper 75 ohm termination and cable shielding.
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For the most part, HDMI is the absolutely worst way to transfer digital audio because of :: 1. PCM audio data "words" are broken up and split between HDMI data transmission words, therefore completely breaking the origination "clock" pulses. The HDMI target device has to receive multiple "HDMI words" at HDMI clock timing and attempt to re-assemble them back into the proper original sampling rate (i.e. 44.1khz, 96khz, etc.). .... and 2. compressed Dolby Digital and DTS is further compressed because of sharing bandwidth with video data. Old school compressed DD/DTS is still much better over digital COAX. The only source that is best for HDMI is the high resolution bluray formats: Dolby TrueHD and DTS-HD MA.
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The exception for using an HDMI cable is when it is used for i2s digital audio in devices such as PS Audio and Wyred 4 Sound DACS/transports. However, in this case, it is no longer "truly HDMI audio". The HDMI cable is just used as the mechanism to transfer i2s data, which is the best way to transfer PCM data. Even s/pdif COAX is an encoded version of the pure i2s source data.
