Hi Bug. This is just my opinion based on what I have read on this forum and elsewhere! Apparently coax is the better route to go as from what I have read there is less coversion involved.
It sounds like the signal is the same, but with optical the digital signal has to be converted to light source before being transmitted and once again converted back to digital on the receiver side.
I have tested both connections and felt that the coax connection gave me a better sound. This could be because I used a better quality coax than optical or maybe because I wanted it to sound better - I am not sure!
Bug, no one has been able to definitively answer this question. Although I have not done a scientific survey, I would suggest that there are just as many people who disagree with Abe's conclusions as those who agree with him. There are just so many variables, type of equipment, quality of wire, distance between connections, just to name a few. You should do what Abe did: test and choose.
If you are using decent cables, then there should normally be no difference. There are some things to take into account though - 1) The fibre core of an optical cable can break if bent too much by a clumbsy oaf. 2) Coax provides an earth connection between equipment - in some circumstances this is unhelpful. 3) Coax is subject to intererence. I've noticed this effect myself and changed to optical to get rid of it.