using the 890FXA lines from both biostar and MSI, and i always have trouble running more than 2. I'm using either 4x5830's or 4x6870's in my setup.
The biostar has alternating pci16x 4x 16x 1x slots. The 16x are red and the 4x,1x are white, the white slots are real close to the red slots so its impossible to put the cards side by side, so i use risers.
Everything is fine as long as im using one from the first 2 and one from the last 2, but when i try to put a gfx card in a red slot then one right next to it in the white slot (with a riser) it fails.
MSI has enough board space to allow all 4 to fit fine (jammed together but fits), but again same problem more than 2 and caput.
I'm using a 1080 watt Xforce power supply it has 4 12 volt rails with 20+amps on each rail, so should be ample power.
The funny thing is when i boot ubuntu on the biostar with more than 2, it frequently has weird behavior like artifacts, and the login window doesnt appear but the purple background does, etc etc.
Anyone have any ideas?