MSI 970a-g46 works good with 1x to 16x extenders
4 5850 sapphire about 480 watts with undervolted sempron
Anyone know how to get 1x working MSI 990XA-GD55 I've tried the pin shorting trick and added a molex adapter.
Asrock 970 Extreme3 I can only get one of the 1x slots working with extender so just 3 slots with this one
Sounds like you may have a bad motherboard. I've had no problems getting both 1x slots working with that motherboard.
I have 7 rigs running 4 x 7970 with the Asrock 970 Extreme3. It's a great motherboard and inexpensive. You can pick it up for $79.9 at newegg.com. You will need two 1x to 16x risers and a custom shelf to hold the two cards on the risers.
I've had a lot of issues with Gigabyte and MSI motherboards and have found Asrock to be better and cheaper.