If you don't mind me going slightly off topic Mark, I was pondering why a USB cable between my Beresford Caiman and SB Touch sounds so much better than RCA. The RCA is a very good quality one but the USB one is the cheapest of the cheap. I guess it must be to do with the USB circuit rather than the cable itself.
Jerry
Hifi: IPL transmission line floorstanding speakers, Squeezebox Touch, Denafrips Ares 11 DAC, DCB1 Pre-amplifier, Croft Series 7 power amp.
Custom Hifi cables HA10SE headphone amplifier and Hifiman HE-400 headphones.
AV system: LG 55B7, Denon AVR -x2300w receiver, Quad 12L (front) 11c Centre and 11L rear . Velodyne DD15 subwoofer.