That sounds like it may be a power regulation issue with your motherboard. Are you using risers? If so, are any of them powered? 4 GPU's drawing the 75 watt limit of PCIE slots can cause stability issues on many lower end motherboards.
Next I would suggest a driver issue. The high CPU usage is indicative of a well known driver combination issue. A quick Google search of known good driver combinations and a comparison to your drivers should eliminate this possibility.
If you have had issues like this from day 1, it is possible its a damaged GPU. To eliminate this possibility remove all but 1 card from the rig, and test each card individually. XFX cards aren't of the highest quality and its entirely possible that mining was too much for one of those cards (GPU's weren't intended to be run at full activity 24/7). In which case you should be able to get a replacement from the place of purchase.
Finally I would suggest swapping out parts individually with one of your working rigs, this will isolate the problem.
I own a mining rig as well (4x Gigabyte 7950, AsRock mobo) and have spent years building and troubleshooting computers so hopefully my experience proves useful.
Hey, Just curious as to what formats you are looking at hosting once you go live? Poker has been a hobby of mine for years and playing for Bitcoin has proven problematic. (seals with clubs has insufficient traffic for cash tables and a tight knit community)
If you have a genuinely good service I think that Bitcoin poker presents a huge opportunity so I wish you all the best.