Question

windows 7 64 bit,  RME 400 firewire interfaces x 3, I get blue screen of death when altering Audio output configuration.

Answer 1

BSOD's are almost always a hardware or driver issue.  You will want to update your driver for your RME 400 to the latest version.  You will also want to make sure that you have installed all of your Windows updates.  Keep in mind that it is possible that you have a failing piece of hardware.  

*I say that BSOD's are "almost always" a hardware or driver issue.  This is because viruses can cause BSOD's as well.