The CPU IMC is an abbreviation for the integrated memory controller.
The memory controller is on the CPU chip thus if the CPU is not installed properly or defective no RAM will work ,in respect to the bank the RAM stick is connected.
Furthermore i have used on the same board with 4 sticks of 1G ,either 4 Kingston sticks either a mix of Kingston and Geil ,no problems were spotted as long as voltage was in the 2,0V area.But i have used the "classic" Phenom 2 and not the X6 which has a different IMC.
On the other hand i could not use them at 1066Mhz with stability ,800Mhz being maximum.
Your issue is very strange and somehow leads to the CPU as being the culprit Maybe the BIOS is not delivering full X6 compatibility.
You can over-volt the RAN a little more as the board will not allow over 2,15V.
So put DDR voltage at 2,0V or 2,1 and try again
The Ganged/Unganged should be there.
Look carefully in BIOS at the Command Rate filed for the memory settings and make sure it s at 2T .
Also adjust the tRFC to higher values ,can t remember exactly but ithink you should use a tRFC of 130 for all DIMM-s .
Also the IMC(NB in BIOS) speed can be decreased to something like 1800Mhz via multiplier ,it may give more stability.
You re left with the need to test CPU in another mobo.If it works there you should upgrade most probable to a new AM3/+ board