I currently own a Yamaha HTR-5650 receiver. The audio input for DVD is for an optical cable. Since I did not have one when I set things up, I used a coax cable hooked from the DVD to the CD input. Should this make any difference?
As far as the digital signal getting through correctly, they are very similar. The optical connection has one major advantage over coax, namely the two components are electrically isolated via their rear panel connections. This may reduce the chances of encountering ground loop problems.
Some people however prefer the more solid feel of coax.
I would rather reduce the chances of having other problems.