Could I use one card as an input and another one as ouput?

I was wondering if I could use one of these things: http://www.dealextreme.com/p/premium-usb-2-0-external-sound-card-box-with-7-1-speaker-spdif-optical-output-27059

which has digital inputs and plug my video console to the optical input, and then decode that sound using my X-Fi modded card as the output to my headphones.

I never tried it so I have some doubts. I only need stereo by the way. Thanks, if you know any other cards or adapters let me know.

That's correct. The ideal thing would be to buy a module for my X-Fi which has the digital inputs, but it has been discontinued for years and it's very difficult to find at a reasonable price. I know having 2 sound cards at the same time should be no problem in Windows 7, and you can select which device you want to "hear" in the recording tab which lists all of the inputs, so theoretically it should be possible to do. But since I have never tried it I'd rather ask first.

Well, I bought the card, turns out it's possible and very easy to do using Windows 7, just select the Digital In in the recording tab of the second sound card as the default device and activate "Listen to this device", and make sure the default device in the Playback tab is from your primary sound card. Sound quality of the videoconsole improved a lot, no noticeable lag for the time being.

I ended up buying it in amazon because I had other things to order: http://www.amazon.co.uk/External-Sound-Card-Channel-Audio/dp/B003TO3KHY/ref=sr_1_1?ie=UTF8&qid=1317849407&sr=8-1 amazing little box. So to sum things up, I connect the optical from the videconsole into the Optical In on this card, and then configure it in Windows like I said before to make my modded X-Fi process the sound.