While I'm a newbie in the headphone club, I have tried many soundcards, including the two cards you mentioned.
The short version: Screw the Audigy, get the Santa Cruz.
The long version:
I have previously owned the Audigy, bought it for a week and sold it right after. First of all, do not be fooled by its 24/96 marketing. This card is not 24 bits at all. While the SNR ratio is improved, it is not over 100 dB (according to a test I know someone did). As for my first hand experience, I didn't like the card at all. It distorts way too easily, especially on the lower freq.
I had to put the sound level to around 50% to avoid the distortions, which is pretty bad. This was done at 50% treble and 50% bass setting. You won't notice it for normal use, but when I tested the card with some heavy bass test tunes, it was obvious for me.
As for the Santa Cruz, no complain about this card whatsoever. I don't know who told you that the Audigy is suited for headphone listening, cuz it's not. I mean, it's not better than the others in this aspect. The Santa Cruz, on the other hand, should give you the best 3D effect on cans, if that's what you want. The sound is perfectly clean as well.
Did I forget to mention that the Audigy will occasionally screw up your PC? It's even a problem Creative has admitted, and yet hasn't found a solution to yet (I think, haven't been following that news for a month now, not really interested....).
So get the Santa Cruz and be happy