Believe me, I've been reading a lot on the forum... started feeling sick yesterday after a few hours of it.
I do remember reading something about re-mapping steering wheel controls. So, I guess then that it's not vehicle specific, I should be able to do that on the Scion. Now, with my stock headunit, the mode button would basically change the source. If I re-mapped that button to VR, is there a voice command that could change the source? Or better yet, is there a list of available voice commands (not just the 5 or so examples)?