Definitely get the soundcard with coax or digital out. Then you can use SPDIF passthrough, the best way to get DD5.1 if you have a receiver. Since most of my media sources are AC3, it's a no-brainer.
Brett, what model Samsung DLP do you have? I know in some of the models (including mine) if you use DVI, it underscans and leaves a black border that can only be corrected in the service menu. Depending again on your model, some (like mine) with lose any service settings if the power goes out...