Like was said, just keep the run short and it won't matter which you use. Optical cables are a little more fragile and shouldn't be bent at extreme angles as to not fracture the glass (plastic in cheaper cables).
The signal being passed is digital ones and zeros. This should have no impact on the sound. Either that information makes it across the cable or it doesn't. If it doesn't, you won't hear much!!
Just a terminology clarification - The SPDIF interface is not coax only. The optical connection is also an SPDIF, just a different connector scheme.