OK, you have the files wrong, it is complaining that you have a stereo .ogg file...
1) Take your source music, and split it into left and right channels, saving each one (* see note).
2) Save in this format .Wav, 44100hz, 16bit, mono (named wasteland2_l and wasteland2_r)
3) Place each one in the rawdata folder of the SDK.
4) Using the SDK fix each file, you know change it to "ambient", quality to 1, volume to 1, etc
5) Take the files out of the gamedata folder in the sdk
6) Place them in your Stalker gamedata/sounds/music folder.
7) Load Stalker and enjoy your main menu playing to the theme of "Ice Ice Baby"
Note : If you cannot split the source audio file into two seperate left and right channels, you will have to take the file and save it once in the format in point 2, then copy the file and rename it so you have two identical files called wasteland2_l and wasteland2_r.
