Cardas Clear or AudioQuest Carbon USB cable

Good call …since you already have CC interconnects. 

Which Cardas Clear USB do you have? the one with one wire or two wires?

If you have the one with one wire, upgrade to the other one: 

I don't recall buying it, but my Cardas Clear USB is a single cable about 18" long.  It's in a setup comprised of USB form Mac Mini to Ayre QB-9 DSD DAC to Ayre KX-5xeMP preamp to a pair of Parasound JC 1 amps driving KEF LS50s augmented by a pair of KEF KC62 subs.  The setup sounds very good even with large orchestrations.

You can upgrade to the better Cardas Clear USB cable. Here is the link: http://www.cardas.com/clear_hs_usb.php

dbphd

Have you ever connected the QB-9 DSD to your C5xe cd player?

If so, did the player out perform your DX-5 DSD universal?

Happy Listening!