I'm having kind of a similar issue where I upgraded the CPU to a T9300 (iMac mid 2007) and now when I try to upgrade to El Capitan it just sits at a light gray screen with a progress bar about 2/3 complete. Should I have updated to El Capitan before I upgraded the CPU?
Where you ever able to get your device updated?
Yes, you need to update to the latest OS first and let it install all firmware updates first before upgrading to an unsupported OS with the patchers.