R9 290X together with older cards?

[tjompen]

An answer in 2 minutes, not bad :-)
Later today my new stuff arrives:
Gigabyte GA-990FXA-UD7
16 mb
FX-8350
a SSD disk
and 3pcs R9 290X

Unfourtnily, I only have 1pcs 1000w and 800w powersupply, and a couple of risers...
Not sure how to connect all this. I have build a lot of computers before, but not with
double powersupplies..

*hope you can read my (old) schoolenglish. This will be fun, though..
I made an test installation with the server guide earlier, works fine. Nice guide, btw..