"Meaning.. the XLR inputs?"
No- bring the outputs from your soundcard to two of the line level channels (or one of the stereo channels) of your mixer. If they go to separate channels (vice a stereo channel), then make sure you pan the channles hard right and left and assign them to the mains output (assuming that's where you monitors are hooked up)
"I can only record 2 at a time?"
Yes- you can treat the left and right sides of the stereo line input on your sound card as two seperate channels. for instance, if you wanted to record two guitars at once, run the source to two channel strips, assign them both to the ALT bus, pan one hard left and one hard right. On the recording software side, set up two audio tracks, one with the left side of the soundcard input, the other with the right.