how can I convert audio in ACA format to WAV PCM?”
Since there is no ACA music format I presume you are talking about AAC, which is the format used by Apple to sell music via their iTunes store. It is actually not easy to convert the files to WAV. They are sold with so-called DRM (Digital Rights Management), which limits your usage – you cannot freely copy them and convert them to any format you choose. However, there is a company that created software called Sound Taxi http://www.soundtaxi.info/ Which can get you rid of DRM protection and convert your music in any format you want.
