External Sound Card for Audio Analysis?

I finally decided to go with a laptop (PC) to analyze preamp and power amp performance. The only issue I am facing now is how to get a good audio signal into and out of the laptop. The laptop only has a combo headphone/mic jack which I doubt is very good in the way of sound quality and I think only has mono input. Therefore, I believe that the best way to go is to get an external sound card that will plug into a USB port.

Not being familiar with sound cards, I am looking for recommendations for an external sound card that will output stereo signals from the audio analyzer software and provide stereo inputs into the laptop so I can analyze the output from stereo preamps and power amps using a dummy load. That means that the sound card input will need to be able to accept 600 ohms from a preamp output and 8 ohms from a power amp output.

I don't have tons of money, but I want something that will give me reasonably accurate results for a reasonable price.



I would say look in Audio Science Review.  Lots of gear heads there with plenty of experience in purchasing and using test equipment to measure audio gear with.
Thanks! I'll see what's there and look for any suggestions from this forum.
Input from Audio Science Review says I need an audio interface, not a sound card. In comparing the two, they are correct.