You should be able to save the digital transport stream as-is, no encoding required. I don't have that particular card myself, but I have (very) briefly used the US/ATSC version of it. What format are you trying to save/record in right now?
One of my friends on the forums here does have that exact card though (the DVB-T version even; he lives in Australia), you may try sending a PM to dug777. I believe he does a fair amount of HDTV recording with no problems.
The only thing I can think of, is that you're trying to save to a format and then later play it in a separate media player, for which you have no audio decompressor (for Dolby Digital or whatever).