Hello I have a similar question. If I have an USB audio interface and plug it into my computer, can one program accept input from that audio interface and another program accept input from the line in in my computer's soundcard? At the same time

The most general answer is NO, you cannot use two sound cards at once. Even if you could, it would just cause more problems. You would have to disable the on-board sound card in the bios to use any add-in sound card (though most motherboards have this set to AUTO so it's disabled automatically, it's best to set it yourself). Check the settings for your sound card, and double check that you're using the right port. Many a time I have either been trying to use the wrong port, didn't have the port set to be MIC-in (some built-in sound cards do this), or didn't have "microphone" set as my recording source (start/run/sndvol32/options/properties, select recording and make sure microphone is checked, then hit OK and make sure microphone has a check underneath its slider.)

Usually, when your soundcard is built onto your motherboard, when you install a "second" one, it just overrides the one on the motherboard. I don't know if that helps out any, but that's what I've noticed.

I also had a similar problem where when I tried to record sound not from a mic but what sounds I "hear" (using Camtasia). I played the video back and it hadn't recorded any audio at all, even though nothing was muted on the windows' volume control. So then I discovered a second sound panel that had installed with the soundcard that was overriding all of my settings on the default volume control.

Hope that helps you out a bit.

For me there is a drop down called Mixer device that lists all the input/output from all of my soundcards (1 on board and 1 pci). Depending on what program you use, you need to make sure you are calling the right input device (in my case... it would be realtek for my particular mic and not the audigy)~

It's always best to DL the newest from the manufacturer's site anyways.

It is. One thing I particularly like about 2 sound cards is being able to toggle (by picking the devices) whether or not I want ventrillo speech recorded when I fraps a game.

Some games/applications don't give you the choice of which sound card to use, either picking one or sometimes attempting to use both. Not recommended for the gamer.

If you have both, and drivers for both, there could be a conflict for the default device for some applications. The fact that it is not selectable what device to use in every game/application means less compatibility, and having both active at once means double the resource usage. I can't honestly approve of it.

Guess it works perfect then!

Yeah, I'd like to add that I am/was running two sound cards as well.  I had onboard sound and an SB Audigy 2 ZS in one of the PCI ports with no problems at all.  Of course, the onboard sound was complete trash, so I had to stop using it, but I only used it for its microphone noise filtering capabilities, anyway.

The only scenario I can think of with two sound cards conflicting is if they're using the same IRQ value or something.