One is for my surround sound, the other for my headset. Lets me have immersive gaming while separating my voice chat easily. I bought the older card when it was new, and when I did major upgrades I bought the new one for the split audio.

I could use the onboard and just use one SB, but ime with onboard it's all trash configurations and half-baked features, so even though this board was $900 I immediately disabled it. I really like the features of the SB cards (and the SB X-Fi line I had before that) and figured the $150 to have something I was familiar with and I liked the audio produced by, so why even bother with anything else.