I have GA-H61M-HD2 MoBo with Intel Celeron CPU G1610 2.6 Ivy Bridge & ATI Radeon 5450 PCIE Video card as main hardware where I have Installed MacOS Sierra (updated to the latest) , Windows 10 X64 Pro and Ubuntu 16.04 running from 3 separate SATA HDD with Clover EFI as the bootloader
Attached are images of my BIOS setup menu for comparison. If the system is properly installed, in addintion to the phantom MacOSX you should see under boot Options, you should also see your UEFI (P.O. SATA DISK Brandname ) in the BIOS Features>Boot Option Priorities>1,2,3.....
I have installed the MacOS Sierra system using Unibeast Clover UEFI USB installer disk with BIOS options as shown in my uploaded images.
Because of my Processor I could not use the integrated Intel HD 3000 and had to use the PCIE add-on Card ATI Radeon 5450 with some tweaks.
I suspect your Intel i5-3450 may be able to support the Intel HD and Multibeast can provide the option under Customize>Graphics menu option checkbox. I am not sure about your Nvidia GTS 450.
I'll try to watch your progress and assist whatever way I can.
Good luck