You cannot use Xeon E5-2690 with a Tyan FT77B7015. That system only works with Xeon 5500/5600 CPUs. (EDIT: I see that you specified the FT77A-B7059, not FT77B7015. AFAIK the FT77A-B7059 is not on the market yet.)
Highly recommend using reference 7970s with that chassis. Non-reference cards like the HIS cards that you have specified do not work too well in this chassis unless you're willing to experiment with passive cooling (see https://twitter.com/jmgosney/status/290391475806695424 )
You will want to use Linux. I only know of a couple people who have tried Windows on it, and they had nothing but problems with it.
Nvidia does have more stable drivers, but Nvidia hardware sucks, so you would be wasting your money.
Highly recommend using reference 7970s with that chassis. Non-reference cards like the HIS cards that you have specified do not work too well in this chassis unless you're willing to experiment with passive cooling (see https://twitter.com/jmgosney/status/290391475806695424 )
You will want to use Linux. I only know of a couple people who have tried Windows on it, and they had nothing but problems with it.
Nvidia does have more stable drivers, but Nvidia hardware sucks, so you would be wasting your money.