EUREKA, my Ci7-950 processor and ASUS P6T finally sees 6GB at 1600Mhz with all setting XMP auto.
My RAM had been stable ONLY at 1333MHz. I have tried three brands of 6GB 1600MHz tri-channel RAM kits, two ASUS P6T motherboards (I had a bad southbridge that was eating up hard disks on the firtst one) and every trick posted on this and other sites.
Today, I pulled the CPU again to verify the pins were all straight, cleaned it and wrote down the CPU information to RMA the CPU. I had read here that the heatsink must be installed from the board. I noticed the builder had not installed the mylar O washers on the top side of the motherboard under the heat sink's feet. I installed them.
When I rebooted, the BIOS noted a new processor had been detected and made me press F1 to enter the BIOS, I set the RAM speed to 1600 on a whim and, you guessed it, the BIOS now sees the RAM as it should.
I have rebooted 10 times. So far, no hiccups. F'in' Magic.