I have exactly the same mb than you and i have no problem with the uefi bios!
I have just instal ######:
- network
- sound with patched appleHDA for alc889
- fakeSMC
and nothing more! No dsdt!
My smbios is for imac 12,2
itry applehda froum last ver of multebeast and not wrok :-( you have alc889 pkg ?