The people who sell super-expensive cables are on the march from Audiophileland to Nerdasia. Are we ready for the onslaught? First up: $500 ethernet cables from Denon!
IP is what we usually send over these cables, error-corrected from end-to-end. This means, generally, that throughput, rather than quality, is what drops with interference or long runs–the networking cards perform integrity checks on incoming packets and ask for re-sends if they're imperfect.
From a standard computing perspective, then, this cable is outright robbery if what you use it for involves ethernet networking, with routers and computers and what-have-you.
This is not, however, what Denon is pitching this for. Denon uses ethernet cable for its Denon Link system, and this means that it tangles up with protocols and streams which are not error-corrected. And it's true that digital isn't the "it works or fails outright" surety that some think it is: you can scramble ones and zeroes just like anything else, if nothing's acting as a gatekeeper at the far end.
Standard Cat6's characteristics, however, allow it hundreds of megabits per second of throughput (they're rated for a full Gigabit), over runs longer than almost any sound system could need. Are we seriously to believe that audio data such as 24-bit PCM and DVD-Audio, will be improved by spending $500 for fancy ones? Over runs of only 6 feet?