Probably they're standard PCM-files...look in your mixer, LordShay, right-click on one of the .wavs and and try if you can "Copy as WAV" --> "IMA ADPCM" ... that's the correct format...
Looked it up
:
Half-Life\valve\sound\ambience\gaol_1.wav
PCM, 11025 Hz, one channel, 8 Bits per sample
Dunno if the files in the .paks are different...