1. According to nVidia, "when PC5300 double sided DIMMs are populated the memory frequencies will be reduced to 533MHz". So the nForce 570 SLIT-A works as design.
2. Please access "BIOS Setup" -> "Advanced Chipset Features" -> "Performance Options" to adjust the following items as suggested & save the changes before exit. The double-sided DDRII 667MHz RAM shall run at [667MHz] then. "System Clock Mode" -> [Expert] "New FSB Speed (QDR)" -> [1066] (or 800/533, depends on the CPU you install) "New MEM Speed (DDR)" -> [667]