Wow, that last link is some interesting stuff! I'm glad to have my statements substantiated. A couple quotes from that page that are interesting:
"the TOSLINK interface of red led is not fast enough"
"That square directly from Toslink receiver is bad bad bad. It is a miracle the DAC reads and understands this crap."
"TWEAKING OF A CD PLAYER to make it a killer transport...Changing the sockets from RCA to BNC or much better to XLR on both the transport and the DAC while changing the resistor from 75 Ohms to 110. "
I have also read feedback that BNC coax is highly superior to RCA coax. That's a given. However, many of our equipment is limited by RCA only connections. lol. I have also read from a posting that the XLR AES/ABU interface is still not as good as a proper BNC COAX. That was based on listening tests and well as some technical justification. I can't remember what exactly they said.
It's proven that there are differences in digital COAX cable. The solid-core silver or silver-plated cables are highly superior because the silver is able to charge/discharge much faster than just copper and it allows better accuracy in the extremely high speed digital square waveforms. One cable I have heard is excellent is the DH Labs Silver Sonic D-750, but at $200 or so for a 2-meter cable, it can be above your budget. I always recommend the Blue Jean Cable Beldon 1694A because it's an excellent digital cable for the money (much better than others if you don't want to spend much). It's documented that 1.5 meter is the minimum/best length because shorter cables will cause signal reflections back to the transmitter and distort the waveforms. I generally recommend 6 feet (which I use).