Okay, now I actually had to go and look up some stuff. For fiber optics, take a look at the Toshiba toslink(Toshiba link)
guide which indicates the various data rates(bit rates)that can be handled. For example, at p.15 is a table of their offerings for digital audio, running up to 15Mb/s. They also show other modules which are used when higher data rates(not needed for audio)are involved. So again, an optical connection is available to carry the data load in whatever the particular use is.
For copper coax, there really isn't a similar max that would have any relevance to audio. For example, I quickly found this
Belden table which doesn't refer to audio, but lists at p.2 the various video data rates in the hundreds of Mb/s, which of course can all be carried over regular copper coax. So, it's tougher to carry light on the inside of a glass fiber than simply guiding an electromagnetic wave down the outside of coax, but either are available to do the required job.
