I was on a 4770k and Bios 1303, updated to 1505 and swapped CPU.
I did reset CMOS etc.
RED CPU LED lit and no Codes or post.
Swap back to 4770k and all is well again.
Now I flashed the Bios using EZFlash inside the Bios, I assume the Bios Updater Program is for doing inside Windows but when you read 1504 and 1505 instructions it is confusing.
http://support.asus.com/download.aspx?SLanguage=en&p=1&s=45&m=MAXIMUS VI EXTREME&os=8&hashedid=EUUwd8jU6IXIucrj
I doubt the new retail CPU is dead so must be Bios causing issue.
Peep with same issue :
http://linustechtips.com/main/topic/169544-new-i7-4790k-wont-boot-on-z87/Edit : I tried running that Update tool from Windows and it updated Bios again to 1505 and asked for a Reboot, once rebooted it entered Bios for me to set up but I could hear my speakers hissing loudly which is not normal.
On booting to Windows my Creative ZxR was gone, I assume the Bios disabled the PCI-Ex1 slot as when I booted to Bios 2 it worked again.
Both Bios 1 and Bios 2 were updated inside Bios to 1505 earlier.