Yeah, pretty cool setup!
Yes, I
did have an iTube, but I found that only certain recordings leant a really cool feel with tubes, while others didn't. Most of my recordings didn't so the iTube just sat there, and I got tired of putting it in-line and then out-of-line again. That's one of the many things about the iDSD Pro specs is that it promises to switchable from tubes to SS. No taking a tube buffer out-of-line: just a flick of the switch.
As for my Auditor, I go single ended, 6.3mm jack. I've tried various balanced headphone rigs, before, with HD800s and either it sounds like the music is coming in one big rush, or it looses some aspect of stereo imagery, or no effect at all. I know there are lots of people who love to go balanced HP in, and that's awesome; I just don't think it's for me.
Now, balanced interconnects are a different story, and I'm really keen on going balanced from the iDSD Pro into my SPL Auditor.
So, I take it you like your rig? I LOVE mine!