I updated my gaming rig and started using my old Asus P5K Pro motherboard (p-35 north bridge) as a dedicated mining rig.  I've individually tested all the risers and gpu's I bought and I know for sure they are not the problem.  My motherboard will not detect a third card.  I've tried tweaking a few things in the bios but had no luck.  Does anyone know if there is a way to get the third (and eventualy 6th) card to be detected?  If not, can anyone recommend a cheap reliable mobo that will run 6 or more gpu's?  I'll be purchasing one tomorrow if i can't get what i have working.  I've let this gpu sit to long not making me any money.
Thanks in advance.

I finally got off my ass and started mining a little more then a month back with my 7950.  Using GUI miner, I found the best thread-concurrency for me was 13,000.  This was independent of intensity or number of gpu threads.  At night i would run 13000 with an intensity of 18 and get 600 h @ 80 C. (increasing the intensity to 20 only gave me 12 more hashes)  While using my computer id run it at 13000 2 threads and an intensity of 12. I had no issues.  Then i got a 280x ( i have a 1000w psu).  I found out GUI miner can't run 2 cards at the same time.  When I tried, both hash rates would run low and fluctuate strangely.  I never let it run for more than a few minutes.  Running the 280 on it's own in GUIminer i found the best thread-concurrency was 40,000 and i would run it at an intensity of 20 24/7 ( i was getting 660 h).  I would have temps ranging from 78-82.  I didn't do much testing on my numbers because it's due to go into it's own private rig soon anyway.

Then i started using cgminer so i could run both cards.  I found the numbers (thread-concurrency, intensity) i had to use to even get it up and running were completely different.  I finaly got both cards hashing at a good steady rate (at and below 80c) and a few hours after that my screen crashed.  nothing but green and blue vertical lines.  I was still able to carry a conversation on Skype with the responsless screen.  I think i fried my 7950...

I pulled it out and put the 280x in my primary x16 slot and fired up GUI miner.  Now the optimum thread-concurrency for the 280 is 13000.  The same as it was for the 7950...  I don't know what to make of this and im afraid to start mining again because i don't want to fry my other card.  Does any know what is going on?

Here is my config file for cgminer.  This is what i was running when the 7950 fried. 

"scrypt" : true,
“kernel” : “scrypt”,
"intensity" : "13, 20",
"worksize" : "256, 256",
"gpu-threads" : "2,1",
"gpu-engine" : "1000, 1100",
"gpu-memclock" : "1250, 1500",
"thread-concurrency" : "10000, 40000",
“gpu-fan” : “40-100",
“temp-cutoff” : “90,90",
“temp-overheat” : “82,82",
“temp-target” : “80,80",