I bought the a40 mixamp, and then a pair of Audio Technica AD700's to use with it. The AD700's are known for their amazind soundstage, which is great for determining which direction a sound came from. You can grab the AD700's for $70 off amazon, and the mixamp is about $130. They aren't a great headphone for music unless you listen to classical, but are legendary soundstage for the dollar.
There are a few mods you can do to them which make them even better. These are the ones I did:
1. put a loop of co-ax cable (or something like it) inside each ear pad to push the speak further from ear (for comfort on longer sessions).
2. elastic around the head pads to help if you have a smaller head.
3. Add a 3 way DIN jack to make the core removable, and allow for mic.
4. Add a 1 way DIN jay to plug a removeable boom mic in (buy a $2 flex boom mic off ebay).
With that $2 boom mic people always comment on how clear I am. The sound is pretty amazing. I generally enjoy using these more than my 5.1 home stereo setup which costs 20x as much.
I also tried the top of the line Tritton's, and they didn't touch these, IMHO. But like rclark says, the a40 kit that come with 'cans' is great too. But cost about $250-300. My setup was about $225 including the cables, DIN jacks, boom mic, mixamp and cans. But the general consensus on audiophile forums (is that AD700's are better than what Astro supplies). It just depends how much you need a mic or how much you like DIY and saudering.
Cheers,
~Shea M.