PLEASE correct me if I am wrong, but locking the dif only defeats the VSC NOT the ATRAC. The ATRAC is what kicks in when the system detects wheel spin and pretty much stops you from both spinning (good thing) and powering through slippery stuff using speed/momentum (bad thing, especially in snow/mud). The only way I know of defeating the ATRAC is manually pulling the plug on the brake fluid reservoir or like a few hard core off-roaders have done, installed an interupt switch to that sensor and then wiring it the cabin.
http://www.yotatech.com/showthread....3&page=17&pp=25
One could just disconnect the plug pictured above immediately before hitting deep stuff, or if it is too late, get out and unplug it and give it another run with all the systems off.
I have tried this before and it does work great. After re-connecting the plug, you do have to turn off and restart the engine to reactivate all the "safety" systems.