From Digital Cable, is Surround Sound same as AC-3?

Is either one captured by standard sound card? If so, any changes or optimizations needed?

If I understand correctly, AC-3 (Dolby Prologic?) will be downsampled by Toolame to MP-2, which on an SVCD in a DVD player will give sort of the effect , best used with Simulated Surround on the amp? Or is all surround sound lost?