Sounds are in the standard FMOD FSB sound bank format, same as used in Bioshock, Bioshock 2, Alan Wake, Dragon Age Origins, League of Legends, etc. There's an extractor at
http://aezay.dk/aezay/fsbextractor that can handle Soma fine.
Models are in no way obscured or hidden away. They are all in the collada DAE format and just sitting there (all 6538 of them). I've loaded a couple directly into Blender fine. Of course the material system is different, but the supplied Model Editor in the soma root directory can show models correctly.
The only encrypted file is _supersecret.rar.