I wanted to connect my Xbox 360 to my X-Fi Titanium Fatal1ty Pro PCIe sound card via SPDIF (optical) to see if I could get surround sound that way. For reference, that card is hooked up to a set of Logitech X-530 5.1 speakers which work great for surround sound in Windows XP and Win7 games. However, the X-Fi refused to decode the Dolby Digital 5.1 signal from the Xbox 360. I was testing this under WinXP using the stock drivers from the CD which came with the card, and it looks like I'm missing the "Decoder" tab under the Audio Control Panel. Furthermore, under the SPDIF IO tab, I cannot select any input options, as that field is grayed out:

I'm wondering if this is a driver issue of some sort. I've also tried using DanielK's X-Fi support pack, but the that didn't change anything. That said, my card has an "Encoder" tab, but that's for a different use case, i.e. if you want to output your X-Fi audio to an external device via SPDIF.

Now, out of curiosity, I hooked up the Xbox 360 to the "Optical In" port on the front panel of my Audigy 1 Platinum (SB0090 + SB0010). That card is currently installed under Win98SE. Imagine my surprise when it successfully decoded the signal and delivered flawless 5.1 surround sound in Forza Motorsport 4. On the Audigy, the "Decoder" tab is present and working, and the "Digital Input" tab allows you to choose what you want to do with the SPDIF signal:

So my question is, can a Sound Blaster X-Fi somehow do this as well? Maybe by using a special driver version or something? I have both WinXP and Win7 installed on the system housing the X-Fi card.