Difference in sound between copper and silver digital cables?

Silver is a better conductor than cupper.  But you can also hear the difference, and that’s the reason why you have to choose between both.
it depends of 2 things: 1: do you like to hear it a bit sharper, detailful?: Ag.. More neutral : Cu. 2 : it departs also from the equipment: how sounds your system: sharp, neutral,dull. You have to find out for yourself what sounds best for you in the entire system. Always search for the best match.: in my system Nordost silver.

Inakustik -- another expensive digital cable. I paid that much for my Synergistic Research digital back in the day, but I'm retired now, ~$300 is my budget.

Is there a difference in sound between copper and silver digital cables, or purely in the implementation?

Yes there is a difference. But implementation definitely still matters.

Take for example Synergistic Research Element cables. Element Copper and Element Tungsten are different only in the two metals. Its pretty easy to hear the differences. This is just as true by the way whether its speaker cables, power cords, analog or digital. Element CTS combines three separate cables, one of each element, and yes what you hear is the best qualities of all three combined.

So there clearly are differences in sound between copper and silver. But compare either SR Element with another cable using the same metal but made by someone else and it will be obvious just how big a role implementation plays in it.

It still boggles my mind that in this day and age we are still talking about digital as if it mattered. Because it doesn’t. Please see above. Wire is wire. How it sounds digital is how it sounds analog is how it sounds between components or the power from the wall. Or inside the speaker for that matter. Its wire. It matters. Wherever it is.

You asked simple question and got elaborates in the answer. Shortly: there is a difference. Shortly: unable to specify which is better because it is subjective. You have to listen. After all... you will find the differences even in the same DAC input types (AESEBU, COAX, fiber, USB).
The cabe is not just the conduit but also the filter. Some cables are better than the same with different length.
If you are audiophile don’t listen the fellows with bit is a bit approach. Let them focus on their consoles and best games. Use your ear instead. If you do not feel satisfaction from the item don’t buy it :)
Is this you or your guests you build your application for?