I am using the board with 3 gfx's, the pci-e x1 slot can be used just fine, but you need to short pin A1 with B17 (
https://bitcointalk.org/index.php?topic=36061.0 ), I used a cable tie (got loads of them whenever I get hardware with cables), with exposed ends, it's been running just fine for 2-3 weeks now.
I tried this too some weeks ago, exactly the same method (a cable tie with exposed ends) but no workie for me.
It does not seem to matter if I short A1 and B17, it boots exactly the same (Linux). I tried the PCI-e 1x to 16x extender on another motherboard and it works there, so that is working. (I even bought 2 of those extenders just in case).
I will try to do some BIOS settings.
(Yes, the PSU is powerful enough to feed those 3 x 5870 cards).