Well, now I have an Abit NF7S board, and had before an Abit KD7, and do not have a PCI soundboard. Both have onboard audio, but the older had Realtek, while the new one have NVidia audio chipset.
I think you pointed the problem, probably FS does not use the same way the 2 brands/evolutions of audio chips.
Maybe I will try to make a new "ghost" installation of FS2002 and copy over the new things, like traffic.bgl, sound, aircraft and scenery directories...once I did it, and it worked well.