For example, dual channel 1600 DDR3 will read as 800 since it is dual channel. OP, your RAM should read as 1066, since it is also dual channel.
Dual Channel has nothing to do with it. http://en.wikipedia.org/wiki/DDR_SDRAM
It's literally as it says: Double Data Rate. In this case, the Bus speed is 800Mhz, so the rated speed is 1600.
OP, as far as why it's not showing 1066Mhz (like it should) I don't know.