The DSS is more hissy than the AX720 and the Mixamp, which can be a dealbreaker to some. With very sensitive headphones, it's pretty audible during quite scenes in games.
In order of least hissy, to most:
I haven't heard the DSS2, but that doesn't use Dolby Headphone. I'd like to try and compare it to the Mixamp some day.
Makes sense, the DSS being cheaper and all. But still, at $45 used on Amazon, it may be worth it for entry-level surround sound. Most amazon reviews (maybe not the most reliable) point out that the DSS2 dropped to a Turtle Beach surround codec that only has 4 channels/directions. I think if I was buying new, I would either go cheap and get a used DSS or go big and get the Mixamp (since I've already got the headphone itself covered). I don't think Astro sells through Best Buy, right?
Edit: BB has the Astro Mixamp BATTERIES (and NuForce Icon DAC/amp), but not the Mixamp itself. So if someone was determined to buy through them, it would be the other two processors or a receiver. Not sure which receivers offer Dolby Headphone, I know my Yamaha has some in-house codec that only makes a small difference. I think. I dunno, my poor hifi stuff has been packed in a box in the basement for 6 months!
Edited by Evshrug - 7/5/12 at 7:43pm