It's simple. If the motherboard runs BIOS, you can't boot from the 3 TB drive. Well, you could, but you could not use all of the drive because you would have to initialize it as MBR.
If the motherboard runs UEFI, you can boot from a 3 TB drive initialized as GPT.
Just went to ASUS to check out your mobo, but the site froze up on me. EDIT: It looks like BIOS to me. So, if I read it correctly, you can't use the entire 3 TB and boot from the drive.