Phenom II processors do not have a memory multiplier available for native DDR3-1866, unfortunately.
In order to get there, you'll have to overclock the base clock (from 200Mhz to at least 233Mhz) and adjust your other multipliers (CPU multi, NB multi, etc) so that they run at the speeds you want (stock or whatever). Additional CPU-NB frequency overclocking will be needed to fully leverage the performance and augment stability.
An alternative to achieving similar bandwidth levels, if it concerns you, would be to lower your timings at DDR3-1600.
FX processors have native DDR3-1866 support.