Gotcha. That will help to narrow down the field. You should be able to find a good 24-bit, stereo card in the $150 - $200 range.
I used a 2-channel Terratec (EWX 24/96) for awhile. I like it. Driver support was good, the quality seemed fine. They have newer models now, but Terratec is one option for you.
M-Audio has been a leader for awhile now. Many people have used the Audiophile 24/96, and the comments have always been positive. Again, that's a model that's been out for awhile, but M-Audio has other, newer models you might consider.
Echo has a very nice, balanced input card called the Mia that i've heard good things about. It's difficult to find balanced inputs in that price range.
I'm sure there are others...
Even if you haven't invested in the 24-bit version of N, you'll see an improvement in quality by using a 24-bit card (at 16-bit). But i'd encourage you to invest the extra $20 (or whatever it is these days) to upgrade N as well. The move to 24-bit is a good one.
There are many other users at the n-Track forum that can give you advice on specific 2-channel cards. I use an 8-channel Terratec and haven't researched stereo cards in awhile.
tj