[cstark27]

Go to advanced and check confirmation and/or delay of around 9s. When active app>fire tv launcher or amazon fire TV launcher or home (can't remember now)>started or in foreground. You can remove the delay and confirmation when you are comfortable with your set up.

Edit: Just wanted to say that out of the box, the mic button and home button both launch the "Home" app. The voice search appears to be an activity inside the Home app. So that makes it harder to set Home button to load XBMC, and the mic to load Fire TV Home. Hopefully I can get to play around with it some more tonight.