Hi spinaltap,

I'm currently using Cardas Clear Light. They were a step up from the standard cables that came with the headphones. Clearer sound. Haven't tested any other with these headphones.

Speaking of balanced cables. Was over at a friends house last week and tested to drive HD800s from the speaker terminals with a XLR cable on a Vintage Yamaha CR2020 receiver.
Improves dynamics quite a lot. So I have ordered a balanced cable from HartAudioCables and will make the end connecting to the amp myself.

Main: Marantz Cinema 50, Meridian 271, DSP7200.2, DSP5200HC, DSP5000 rears, Meridian 210.
PC/Headphones: Mytek Liberty II, Sansui CA-F1, Sansui B-2301, Sennheiser HD800, Kef R3