(In reply to comment #50) 
> You'll need to use vga-switcheroo to select the card you want to use.  Then
> you should be able to start X without any config and it will start on the
> one selected by vga-switcheroo.  Having two device sections as your config
> does will force X to try and start on both devices.

I tried without the BusID but all I got was a black screen. For some reason
when I switch to the intel GPU I get a black screen also, though it did work
when I booted from grub-efi earlier with the well documented outb commands to
disable AMD (no BIOS from EFI w/o efistub). Not sure if it's an issue with
vga-switcheroo, intel driver or something else.

I don't know if it's a problem, but both cards are powered on at boot. I can
switch back and forth between the GPUs (though it's tricky doing so blind when
on intel graphics).

Any other suggestions? Thanks.