I see you have linked a 5670, was there a reason you chose the 5670 other than trying to stay compatibility with the hybrid setup?
I am afraid as someone else has stated, that the hybrid setup anyway - would not be compatible with the 5670 - Only the 4200 series would be compatible with a hybrid setup, and again, there are so many better options out there since the release of the 4200 onboard chipset. (That is what I believe the 700 series AMD chipset has for an onboard GPU)
I looked at both a 5670, and a 6670, and based what I would recommend for a gpu, I looked at the price of what you selected, your use of your system, and also, kept in mind
if you have the desire to do light gaming; or if your needs change, the card should suite your needs.
Check this out:
http://www.newegg.com/Product/Produc...82E16814125403
This is the 6670, which out performs the 5670. It has an updated gpu chipset, it's cheaper, and it should be adequate for your expansion needs. I would definitely go for the 6670 rather than the 5670.
I would hope someone else could chime in as well just to give you an another opinion, and it would give you a better selection as well.. If not, I am confident, that this GPU would suite your needs and keeping it's scalability open if your needs changes down the road..