two types of digital on sound cards: 1) optical via toslink, and 2) coaxial via RCA plugs
the santa cruz, which i own, has a versajack is actually a mini-stereo jack, so u need a 3 dollar stereo-to-RCA cable or adapter...i have one, works fine, but that's still coaxial
if u're looking for optical, and dont' need 5.1 analog, i'd get the hercules fortissimo II...i find it one of the best values out there right now w/ both digital in and out via toslink, 4.1 analog, and a dedicated headphone jack.
the yamaha based cards otu there (i.e. the aopen ones) also have optical out...some of the extremely cheap c-media cards (i.e. zoltrix nightingale pro 6) also have optical out.
the hercules GTXP has it, the audigy platinum has it, the terratec DMX 6-fire, and a bunch others.
EDIT: i should mention, u don't need a "5.1" sound card to do 5.1 out via AC3 pass-through to a dolby decoder...the 5.1 label just means 5.1 analog, u're doing 5.1 digital..any card sporting digital out can do 5.1 via pass-through