Domenico is right, you can load .INS files only, and it will take on RAM the size of the .INS file. So, since these files are uncompressed audio they are loaded as is.
Here is the waveform of the stereo piano.ins loaded as raw pcm data, you can see it's totally uncompressed (playing it I think it's sampled at 22050Hz, since if I play it at higher sampling frequency notes sounds too high).
http://www.4shared.com/file/89421025/c363c0d/wave.html