I realize this is an older post, but to help others that may be pulling their hair out......
I recently recieved a P6T deluxe v2 motherboard with a bad Dimm channel (B1 to be exact).
like the original poster I tried every combination of memory 2GB X3 sticks (g.skill ddr3 1600 - cl8 - qvl approved). I'll post my basic trouble-shooting to arrive at this conclusion.
1. try 1 2GB stick in slot A1 = "usable Memory: 2048" - good
2. try 2 2GB sticks in A1, B1 = "usable Memory: 2048" - not good
3. try 3 2GB sticks in A1, B1, C1 = "usable Memory: 4086 - not good
4. try working module that was in A1 in B1 by itself = no post - not good
5. try known working module in slot A1 again, with module that was in C1 in B1 now
= "usable Memory: 2048" - not good.
6. try 3 2GB sticks in A2, A1, C1 = "usable memory: 6144" -good
--> problem with using slot A2 is that that stick will only be used as dual channel until all primary (A1, B1, C1) are used.
( I got high performance mem, so I want slot b1 to work)
the common denominator is that B1 flat doesn't work in the system info screen under BIOS.
it doesn't matter what operating system you try and install if the BIOS won't recognize it, it's probably a bad memory stick or bad slot - in my case it's a bad slot because the memory all works in other slots.
I also tried updating to the latest ASUS bios (0302) and it didn't help.
I've RMA'd my board and should have the replacement shortly and i'll post the results....