Yes, those are the units Creative labs is selling directly on ebay and they will indeed decode AC3. I'm using one right now with my Pansat 2500A and it works. I didn't buy mine directly from creative labs however. I bought it from another seller who bought it refurbished from creative labs on ebay and then after using it about a year sold it again on ebay. I believe he used it for some other purpose like digital recording on his PC and later moved on to a higher end product. Anyway, the extigy will work. You'll need analog speakers to connect to the outputs of the Extigy. It uses the little 3.5mm stereo jacks like computer speakers and headphones use, but you could probably use an adapter cable if you needed different jacks. You probably need to use amplified speakers as I don't know whether the device could really effectively drive unamplified speakers directly.
As for the Durabrand units at Walmart, be careful. while it is true that at one time there may have been one durabrand unit that Walmart carried that had a spdif input and would decode AC3, I believe all of the cheap ones they carry now do NOT and only have analog inputs. In fact, before I bought the Extigy this is exactly what I bought only to be dissapointed by the fact it wouldn't do what I wanted and had no spdif in. After that I bought the Extigy after I saw on another forum a post saying the Extigy would do this. Anyway, now I have the Extigy decoding the AC3 from the Spdif out on my pansat and feeding analog out to the durabrand speakers.