silver vs silver coated digital coax?

The frequency of the signal being sent is the key.
The lower the frequency of the signal, the deeper it penetrates the surface of the wire.
For Video frequencies, the depth of penetration is rather shallow, so plated wires work fine. For Audio signals, the depth of the signal into the wire surface is DEEPER than nearly any plating, and solid wires should be used in hi-end applications. (when the signal has to move through the plating/core it will add distortion to the signal.. in theory)
A digital signal is probably near the video frequencies, so a plated wire 'should' be ok. However, with the BIG DEAL about 'jitter' I would use only a 'solid' or nonplated wire.

I was using a 1.5m DH Labs D75 which is a silver plated coax and recently upgraded to a 1.3m pure silver Oyaide coax. The pure silver sounds smoother and more relaxed, removing a subtle but persistent brittleness from from the midrange and upper treble. Bass notes also became rounder and with slightly looser.

Some wires promoted as "silver" are actually silver plated. Don't fall for this.

Save your money, son. The electrons neither know nor care. Go to MonoPrice and snag a very nice coax cable for about $10. Send the money you would have spent to a worthy charity or help out the homeless guy who is sleeping under the bridge near you...

-RW-