The Archos Player (and Recorder) are what we call "hwcodec" targets. They have special hardware for decoding the audio, rather than doing it in software.
Though we're able to make this player play WAV, special code has to be loaded into the hardware, the MAS, to do so. Right now this is handled by a plugin, and is not part of the playback system. So, WAV playback is limited to a single file at a time.
If you want a player with digital output that's capable of playing WAV (or, even better, FLAC or other lossless formats) you should look into the H100 series, which have an optical output but decode in software.