I am trying to set up Audition to be able to record from playback from the computer, as well as a usb mic. I have a Dell XPS 8300 with Realtek High Definition Audio. What kind of a sound card should i get that works well with Adobe, and could handle multiple audio inputs and be able to record from playback in other programs on my computer?
Whilst there are plenty of external sound devices around that will let you use multiple inputs successfully, some of your other requirements are going to cause you problems, especially with a Dell. For instance, the chances of getting a USB mic to work alongside an external interface - well it's not impossible, but to say the least, you're unlikely to get any sort of trouble-free result. This is because you are going to have to use an external driver (like ASIO4ALL) to merge both devices into something that Audition can recognise. We've been asked quite a bit about this before, and nobody's ever come up with a truly workable solution.
Generally, the thing to do is to get rid of your USB mic from the system, and plug a proper microphone into a suitable input on your sound device, and record it like that. This gives you other useful things as well, like the ability to monitor what you are recording on the external sound device headphone socket. One of the problems often encountered with Dell's approach to the internal sound device is that they simply won't let you do this - they think that there's a danger of feedback occurring and that all their users are too stupid to be able to do anything about it...
And Dell's other problem (although it's by no means limited to them) is that they've been got at by Microsoft and the RIAA. The effect of this is to make it incredibly difficult to ever record the output from any other program - because they insist that all of this constitutes piracy, even though there are loads of legitimate uses. So they disable 'what you hear' as a record input internally. There are ways around this using something like Virtual Audio Cable, but they aren't easy to set up. It's ridiculous - the audio equivalent of disabling Cut and Paste...
What all this amounts to is that you, as a naive user, purchase a computer thinking that it will help you with what you want to do. So you ask sensible questions about it, and discover that the answers are anything but sensible! Most of these things are solvable, but only with some considerable effort on your part, and possibly a little rethinking.
What's the end result you are trying to achieve? It's often easier to point at specific solutions than general ones.