First of all....for all intents and purposes, most all AM3+ mobos can run 1866 - the big thing that matters is can your CPU and even more so can your CPUs MC (memory controller) run 1866....regardless of AMD's 'marketing' the FX CPUs can run 1866, but with most it takes a serious OC...the 8350, 8150, 8320 and some 8120s generally can carry 2 sticks of 1866, after that it's hit or miss, some 6300's can others can't, most 4100s simply can't
What you can try is enable XMP, then raise the DRAM voltage + 0.05 over spec (so if 1.5 sticks go 1.55), and also raise the MC (memory controller) voltage up initially to 1.3 (may take more or less), MC voltage is normally referred to as CPU/NB or CPU NB VDD