Which card do you have? Most cards since the Audigy 2 do NOT have a decoder module, including most X-fi's.
I am using the PCI Express Sound Blaster X-Fi Titanium Fatal1ty Professional Series. I am aware that it does not have a built in decoder, and I am also aware that the "champion series" does not have that built on either.
Do you have any suggestions as to what I can do... perhaps like a software decoder?