Thune, I didn't know this was a competition.
I heard both of them. My impressions on the Teton are in the Teton thread that's currently linked to the front page.
The one sentence version is that the Teton is really fast, as in dynamic and detailed and not murky.
As far as the ALO Studio Six, my impression at the time was that it really brought out the bass on HD800s. I would go as far as to say that is an absolutely killer combo, and if I was looking for an amp for HD800s, the Studio Six would be at the top of the list. I suspect, would bet even, that they tested those two together during the development stages.
This may be a side point, but the smaller tubes in the Studio Six have glowing orange gas in them, and look really cool. Like tiny little lava lamps or something.
As far as a comparison of the two, I think it all comes down to synergy and a little bit of personal preference. My guess is that the Teton would be a great match with Tesla series Beyers or just about any orthodynamic. I personally thought it was a little bright with HD800s though. The ALO Studio Six, on the other hand, was as I said really great with HD800s, and has great tone and warmth.
To be clear, neither of the two amps sucks in any way. It's all just a matter of which headphone you want to pair them with and what sound signature you prefer.