That reverse-engineered codec is the same one SMPlayer2 uses to play WMA on the Pandora. The Audacious PND is just too old. (It's either too old an FFmpeg or a version of Audacious from before the FFmpeg plugin stabilized enough for them to stop hard-coding the list of accepted formats.)
There's also a full list of what they reimplemented in the current version of FFmpeg. (It only requires external dependencies if there's an E in the "decoding" column. If there's an X, you're fine with a suitably recent version.)