dub Beatz, thanks.
I'm currently not gaming but in the future when I upgrade my PC to game again, I will definitely consider the AD700 (and A700 (see below).)
What about in terms of movies and music? Would you consider the HD-555 better in these departments?
First question: In my opinion, the HD555 would probably be better for just music and movies. The AD700 have a detached sound signature that puts the wearer in a room where the sound stage is at an accurate distance, rather than on top of him or her. Because of this, they are less engaging headphones. The HD555 are said to be more engaging and in your face when compared to the AD700. I have watched movies on the AD700 before but was never blown away. It just didn't feel very fun watching movies through them. They are great gaming cans, and just good at the other stuff.
Second question: I wouldn't expect the audigy 2 to perform well in the gaming category. It's a very entry level card, and I don't even remember if it uses CMSS 3D. I think it's just a music and movies card. Since you don't game, I don't think there will be much a problem driving the AD700s out of your Audigy 2. The AD700s are very easy to drive and sound fine straight out of my iPod.
Third question: I absolutely adore my Beyers. I got them because of the advice of a member on here known as Mad Lust Envy. He's big into gaming as well. The reason I decided to upgrade was because, like I said, my AD700s were getting boring. They are absolutely incredible when it comes to positional audio, but they lack a certain wow factor, and just get boring to listen to. They had sharp highs, a tight but very lacking bass and because of the soundstage everything just seemed detached. I went around looking at the options for upgrading and was sure I was going to get the DT880s, until I read the suggestion of a friend of mine, being Mad Lust Envy. He purchased the Beyerdynamic DT770 pro 80ohm headphones and hadn't even used them for gaming until one day. The experience he described to me sounded like it was just what I was looking for. A pair of headphones that gave me the wow factor. Paired with my X-Fi forte, they gave me a theater like gaming experience. The bass is killer on these babies, and everything is so lush and warm. They don't have piercing highs and are just a blast to listen to. I got these headphones and immediately began gaming again, and let me tell you, Battlefield Bad Company 2 was an entirely different game with these bad boys on. It went from a first person shooter to a "holy sh*t is this real life?" shooter. The audio was absolutely just so much more engaging. Maybe it's the bass, maybe it's closed factor and reduced soundstage. Whatever it is, I love it. Here's the best part, my musical preference being hip hop (underground 90s, not mainstream trash) and electronic dance music were these can's forte. Electronic and hip hop sound incredible through these babies. Not only that, but if I want to watch a movie, I put my card in game mode for the CMSS 3D and they turn into a surround sound theater. I love these babies with all my heart. Here they are, and also just take note at how incredible comfortable these headphones are. http://www.amazon.com/Beyerdynamic-Pro-80-Closed-Studio-Headphones/dp/B0016MNAAI/ref=sr_1_1?ie=UTF8&s=electronics&qid=1292296480&sr=8-1
Fourth question: The difference between the AD700 and A700 are the fact that one is an open headphone and one is closed. The AD700 is an open headphone, meaning there is no closed back to the driver, so sound leaks out. This is said by many to create a more natural sound, however, because of the open factor outside noises also seep in. Not to mention the fact that others can hear what you're listening to. It's not that bad though, I promise. The A700 are closed back headphones, and you can probably guess what the advantages to that are. If you were gaming, I would say grab the AD700. For music and movies, the A700 are great headphones, plus they are closed so you don't have to worry about others bugging you or hearing what you're listening to. Sonically, I'm not entirely sure what the differences are. I've never auditioned the A700s. From what I've read however, they are great headphones.