1. EAX 1.0/2.0 and A3D 1.0. I don't know how well it works with A3D, as I don't believe I have any games with A3D, so I have no been able to try. It works well with EAX, though I have been noticing some oddities. For example, in Unreal Tournament, the sound is extremely muffled whenever you're in a tight area. Crouched under a staircase, or even crouching on a snipers ledge somewhere. I understand that it should sound muffled given it's such a small area, but this is REALLY muffled. Even the "Head Shot!" voice is muffled. These instances are fairly rare, though, and I'm sure it will be corrected in a patch.
2. Not sure on the DD decoding. I've never had a decoder card, or a receiver, so everything's always been done within my system. It seems to work superbly for me so far. Each channel is distinct and clear.
The card does have a Digital Output jack. They have this nifty thing on it called the VersaJack, which is basically a 4-in-1 jack. You can use it as an Analog Line, Digital Output or Analog Line Input, or Headphones Output. Just plug any of those into the jack, and change the appropriate setting in the Santa Cruz control panel, and it will work for it.
Chances are they will be coming out with a daughter card for it, though. They've certainly left the card open for expansion.