Beat,
I've had both the CIA and a Nixon Tubedac. For me it's not really close. I ran through about 5-6 dacs in a period of a few months and haven't even look at a DAC ad since hearing the Nixon. The CIA was bettered by an EAD DSP 7000 III and the DI/O Mensa, but the Nixon was, for me, way better than any. In terms of emotion, detail, realism, accuracy. The Nixon has it and more of it than the others. I don't think I'd be too bent out of shape about throwing into an all tube rig either. Give Scott a call and talk to him, the tube doesn't play much of a part - which is why tube rolling doesn't yeild huge benefits - some yes, but huge, no. It's certainly not like rolling with a preamp or amp. In any case, try and get hold of a Nixon and give it a listen. I think you'll be glad you did.