one thing to check on the miniDV is whether it is in the 12 bit or 16 bit audio mode. some cameras default to the 12 bit setting and that may be the cause of the poor reproduction.
I had a similar problem with my Panasonic PV-GS300. I had to simply set my camcorder to playback mode before plugging in the USB to the computer. I have no idea why the "connect to pc" mode would not work for video - this mode would only work with my...
I think the best way is try to get the video camera with the same brand for playback.