In case anyone else hasn't noticed, I discovered several days ago that TV3 (DVB-T) was broadcasting with AC3 audio in additional to the normal AAC stream. And, as of 6:49 am this morning, they are still doing so. I'm using DVBViewer 18.104.22.168, by the way.
So far, I've only been able to get the freeware AC3Filter to decode the AC3 stream. However, I do have the Cyberlink PowerDVD 8 codecs on my system - which should handle AC3, if I read the Help correctly.
AC3Filter is available here: http://ac3filter.net/projects/ac3filter