No AC-3/5.1 using generic backup

Can someone help! When I select generic mode save to HDD and specify AC-3/5.1 using generic, the playback is not decoded correctly. I’m using ffdshow with my HTPC and S/PDIF sound card. All settings are correct, any ideas?
Thx
Bnw

how are you playing them? in a mobile device or on your computer? what device or what media player are you using?

vlc media player is what i recommend. http://www.videolan.org/

From memory I think Vista needs to have AC3 Filter installed to work properly.

what? like this http://ac3filter.net/