SonicStage needs to be installed regardless of what other decoders you use, otherwise this won't work. To use any of the methods here you also need to activate the "Decode audio files with SonicStage (must be installed separately and requires Media Engine)" option in JPCSP, which is located in Options > Configuration > Media.
It's not worth it though, as the previous method supports more formats and doesn't require any hacking to set it up (plus it's made entirely out of freely available files). It goes into the same folder as atrac3plus2wav above. There is a third decoding method which uses the devkit encoder/decoder accidentally leaked by game developers, at3tool.exe, but to use it you need to own " Fate/Extra CCC" JP version and use several specific hacking tools to unpack its archive. The extractor is closed source and its author isn't available to get any permission from, so for now it's also not bundled. The driver is copyrighted, and so even though it's freely available in the trial version, it can't be bundled with unlicenced open source software like jpcsp. Next, move both " atrac3plus2wav.exe" and " atracplug.dll" to your jpcsp folder, to l ib/windows-x86 for 32 bit version and lib/windows-amd64 for 64 bit version. Close the installer now that you got this file. Open this with winrar, winzip or 7zip, find a file called " atracplug.dll" in it and extract it somewhere, like the desktop. Once that happens, alt+tab out of the installer, open windows explorer (either with desktop icon or windows key+e), navigate to " C:\Program Files\Sony Setup\Sound Forge 9.0" or " C:\Program Files (x86)\Sony Setup\Sound Forge 9.0" depending from your system, and find a file called " atracplu.cab".
Once you have it, start installation and press "next" several times until the program asks you to install Microsoft Visual C++. It has to be 9.0e build 441, any other version will crash the program.
To get it, visit SONY's website ( ) and download the " Sound Forge 9.0e Build 441" trial version. This is the program that will do the decoding itself, called " atrac3plus2wav.exe".