I haven't done alot of digital cable swapping, so I can't comment on the importance of hyper-expensive digital cables. I would say, though, make sure you use a cable designed for digital signals, and not some rebranded analog cable--the digital "signal" is a very different bandwidth and using analog cables will cause a hardening and rolled off sound in my experience. I suppose this is probably related to attentuation of parts of the signal, but also to jitter.
I personally listened to 4 or 5 digi cables and just settled on MIT AVT1 for my "reference" cable. It sounded as good as anything else I tried, is well-built, works just fine, and isn't badly priced to boot.
Right now I am using the digital cable that came with my ack dAck! 2.0, and it works fine, too.
Analog cables, OTOH, make a huge and very noticeable difference.