I have things working, and using Andre's suggestion of setting Max_Audio_Channels to 1.
At least a couple of times, I've noticed the Simshaker/Buttkicker stops working about 1/2 way into my flight. Not sure why it stops. things are working just fine, and then no more vibrations. I'll dig through this thread to see if it's a config change of some sort I need to make.
My SB Z sound card is only used by Simshaker and my Buttkicker, nothing else.