"surround" or "THX" cards
As a golden rule: stay away from anything that has "surround", "7.1", "5.1", "THX" or "cinema" in its name. They all translate to "end consumer crap" and are next to useless for production or DJing purposes. No matter how many IOs and shiny features they might have!
Be sure to buy hardware with ASIO support and at least two analog, separate stereo outputs instead, if you are a Windows user, look for CoreAudio if your bread is buttered on the Apple side or Jackd, if you should use Linux.
You can get a decent external card for DJing for about $100 - you do not need a lot of mic preamps and sophisticated inputs. These things are for recording and that's not your primary intent (if at all) as a DJ or producer.
Cheers and have fun,
Tom, live act, producer, VJ, DJ and wtfnotelse
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http://soundcloud.com/ax11