I don't know. I haven't heard someone tried such a thing. I think it would cause distortion and conflict. Is this just a question or are you trying to hook up a system with two sound card? This happened with my on-board and sound card in my rig. I have to disable the mobo's on board audio to get rid of the distortion.
I play the same audio between two seperate sets of speakers. One set amplified externally, the others are default to some cheap speakers in my workshop. How I can connect to outputs to one output. I don't always want the neighborhood to hear what I am listening to but when I have a BBQ I want to use the externally amplified speakers. So; how do I use to cards or is there an inexpensive 'switch' (and I mean inexpensive - obama is getting more of money).
Windows 7 has no problems with multiple sound cards. The notification area Speaker icon even gives you seperate volume controls. The key is using a player that allows you to chose which sound card to use. I use MediaPlayer Classic - Home Cinema to play .avi and .mkv and dvds over hdmi from an Auzentech X-plosion while the on-board Realtek connects to speakers with a headphone jack. I can still surf and play music or watch YouTube vidoes while the family enjoys video. I think this should be a standard feature on every HTPC.
You can INSTALL two sound cards, but you can only have one input and one output at any one time.* Even using the input from one device to output to another device is dicey, and depends on drivers playing nicely together. [I'm looking at you, Creative]
Really, the best option is just ot get a card with all the inputs/outputs you need.
*The only exceptions are programs that let you select which card is the input/output, but I've seen some crazy things happen with some setups like this. And most programs do not give the ability to use the non-default windows sound device anyways...
My system default is the on-board audio and monitor. Output is speakers with headphone jacks for private listening. Everything is seen and heard here EXCEPT the extensions you chose (.avi .mkv .vob) to associate with MPC - Home Cinema. Set MPC -Home Cinema to output to the second sound card and for the video to play full screen on the TV which is connected via HDMI.
The movie plays totally independant and without interruption from anything else I'm doing on the computer. I can use Skype, YouTube even play a second movie on the moniter with VLC (listening on headphones, of course).
If you add VLC and MPC-HC to your SendTo folder you can view any file on either screen by right-clicking the file and selecting a player.
Wow. I'm surprised to see so many ppl having problems running multiple sound cards. I have 3 in my system ( only because one goes to a mixer, one to a set of surround speakers, and one to studio bookshelf speakers )....i have no problems whatsoever picking a choosing input and output devices between cards and I'm using Win 7 Ult 64. Maybe because all three cards are identical I imagine. Anyway, you can have as many sound cards as you're mobo will hold, but only one can output a specific audio channel at one time.