OFP supports wav, wss & ogg - enough for most purposes.
However, it doesn't play the files directly, each one has to be configured (in description.ext) as a sound object. The script then calls the object, not the file. As if that wasn't enough, the sound can be configured in different ways e.g. as sound, music or radio, each with its own peculiarities.
OFP is also a little sensitive about the formats of sound files. You may also have a problem with your sound conversion software - getting compressed files longer than your raw files seems a little odd.
You do need to go to the Editor's Depot and get Bloodmixer's Sound Tutorial which is how most of us started.
Regarding the 'soundpacks' - some may contain wss files because they are meant to be direct replacements for the original BIS wss files that came with the game. If you just replace an original with a new one of the same name you wopuldn't need to configure it because it's already built-in. Just a guess though . . .