https://www.amazon.co.uk/Amazo…3012&s=electronics&sr=1-1 that is the one i purchased...im still new to S/PDIF so im tredding un-familiar ground when it comes to "correct" cables.
I had a look at this and pretty sure it's just a normal cable used for Hifi connections. Amazon do a Digital Co-ax cable here:
I could also suggest these that I bought on Ebay :
No guarantee that these will cure your problem but at least you'll know you have exactly the right kind of cable ....
If this doesn't fix things, you could also give the guys at Focusrite a call.
I had a weird problem with a soundcard of theirs and after emailng them for support, had a very helpful telephone conversation from them