pcm is pulse code modulation. Means it can only pass decoded info out of the card through a digital port. AKA you can't pass the raw dolby digital info out of the sound card to have a reciever do the decoding.
X-530's are analog speakers, meaning you don't have to worry about digital encoding at all. I don't know why they lable these as "Dolby Digital", as you could pipe DD, DTS or THX through them and they wouldn't care (all the decoding is done in the sound card).
Your sound card has ports for all the channels the speakers want, so hooking them up is as easy as matching plugs to ports.
As for decoding.....this depends on what you are trying to do. If you are trying to watch a movie in DD 5.1, then the software you use to watch the DVD will need to have the proper decoder. The only other application where digital decoding would matter would be some games. I don't have much experience with digitally encoded games, but there probably is an option in the audio section to turn off DD encoding. This doesn't mean you won't get 5.1, it just means that you aren't passing it as encoded data.
edit: I just checked far cry which is a DD game and it has a setting in the audio for Dolby 5.1 and just plain surround. You would want to set it to surround which will keep all the channels discrete (instead of lumping them together via the DD encoder). You will lose a touch of quality and it's a little more processor intensive (DD is a compression tool), but you probably won't even notice the difference.
