I shouldn't have said "encoding", I should have said "compression". My mistake.
What I meant was that it can't be converted by something like WMP's little audio converter. I believe the programs on the computer are able to play them because it is gathering data from FS in order to do so. I haven't tried putting the unconverted .wavs on a comp without FS and playing them...
If you try to convert them, you'll get a message like "Unable due to unrecognized codec", even though the same program can play them flawlessly.
Like I said, Goldwave or a similar program can convert them.
I actually have very little knowledge about audio encoding or anything similar. I had to have it explained to me: here, I found a quote from my (very old) thread:
IIRC FS2 uses wavs using MS ADPCM compression. Something like Goldwave should be able to convert it (Or at least turn it into an uncompressed wav).