I have the same problem, and I have tried every setting I can think of. I even tried transferring the recordings to a FreeBSD machine and playing them with mplayer. Still no sound.
I have a mercury Tv card. It is working ok but I can't save audio when recording Tv programs. I have done all the steps indicated in the user manual without good results. The following note appear: cannot render audio capture stream
and in the 713X Chip Audio Settings (audio settings box) some parameters are grayed out and the parameters standard and format indicate ERROR
Please, I need your help. Thank You