My diy DAC connects to a modded Denon 3910 that exports CD (I2S) and DSD (SACD) via a CatX Ethernet patch cord. I also modded a Squeezebox Touch to export I2S to my DAC via CatX patch cord. While this setup isn't common, I figured it was worth sharing. I2S and DSD have separate clock and data where clock is embedded in the SPDIF signal; some folks feel the SQ with I2S is better. I2S is how the transport in your CD/SACD player gives data to the DAC chip. I had no issues with redbook from the Denon or standard flac or hi-rez files from the Touch going to the DAC, but experienced dropouts or static every now and then when playing DSD on the Denon with one of my patch cords.
I wasn't using real cheap Cat5 patch cords. They were stranded twisted pair, shielded cables. I even cut them up for hookup wire in some of my diy projects. I decided to try some Blue Jeans Data Cables.
They offer certified Cat5e, Cat6 and Cat6a cables. They test the cables they make with a Fluke DTX-1800 and provide a printout with the cable. They provide a page to understand the report.
I went with Cat6a as its rated for 500MHz; the two flavors of DSD are 2.8MHz and 5.6MHz. While not cheap they didn't break me. A one meter Cat6a ran me $14.50 while the two meter was $17.25. Color choice for my cables was blue or black. BJ says "For Cat 6 and 6a, Belden doesn't sell patch cord stock in its standard catalog (the cables you may be familiar with are designed primarily for "horizontal" use), so we've asked Belden to manufacture special patch-cord-optimized Cat 6 and Cat 6a cable stocks for us which we terminate and sell under the Blue Jeans Cable brand. With all of these cables, we use Sentinel brand RJ-45 connectors, manufactured in York, Pennsylvania."
While I cannot detect any difference in SQ, I have no issues playing DSD (SACD) from the Denon and feel it was worth the small investment and peace of mind.