I think elementaryOS is not linux but an ubuntu based distribution.
Any how, you should install the grub bootloader on sda6 alone.
I had done it before, see below. I only have 500GB and partitioned it.
I had tried Luna(grub bootloader) on it, following this guide and successfully made it worked.
Im now experimenting Quad booting on my Fujitsu, currently Chameleon can see and boot on Fedora.
Wndows81, Yosemite, Fedora and Arch Linux using Chameleon as the main bootloader.
Which partition is your default 1st boot?