The generic.PlayWave(...) method should work with WAVs on MC40. I have attached an example page which works for me. Unzip the zip file into the root of the SDcard and load the playWave1.html file as the start page.
One reason why it might not be working for you is that the root of the SDCard is treated as the root of the device. So the wave.wav file in the SDCard will be referenced as:
TestPages.zip 521.3 K