The same exact thing happens to me. I'm using the Nvidia 9755's (built and installed using the "envy" utility). Whevener I try to "Start Media Center", it removes the drivers, asks for the resolution in the initial configuration, and then the machine hangs completely, requiring a hard reset. Upon reboot, I have to reinstall the drivers, for X won't load.
I'm stuck. Tried inserting an "exit" in the beginning of Config_Device_Changes.sh, no luck.