Sorry, don't know if we're allowed to answer here, but I will anyway.
The easiest way to convert to .wav is to open the file in Media Player, and click save as, then just rename the file to filename.wav.
To get the right compression ratio, open your .wav with sound recorder and change the settings there. I'm not fully sure this will work, because my sound recorder doesn't work for some reason, but that's irrelevent.
I will warn you though that I am one of the people who lost all the RCT sound files, so I don't recommend it. I got them back by re-installing, but I lost all my custom scenery. But it's obviously your call.