I tried Grisp and Grisc on some of the audio only .SNM files but they would neither play nor convert. I tried the files out in XWA Cut Scenes Player and the files played for a few seconds then stopped.
As far as I can gather SNM is a later version of the .SAN format. These were the Variant 2 VIMA.
http://wiki.multimedia.cx/index.php?title=VIMA
Is it possible to convert these to a wav file ?