I thought the FX55s Multiplier was also unlocked as the other FXs are, simply set the CMOS settings to manual instead of the AI, and increase the multiplier,,, 2.6 is a 13X multi, 2.8 is a 14X, 3.0 si a 15X, Etc.
You'll have to increase the V-Core to run higher multipliers, but everything else stays in spec, make sure you have good cooling!!!
Watch the V-Core carefully as ASUS M/Bs run those voltages higher from the git go, you should be able to hit a 15X multiplier around 1.4v, but use that information to sneak up to where you want to go, don't try to go straight there.
You probably won't get past 3.0GHZ on air, you have to keep it cool, thats the most important thing!!!
I had my FX57 @ 3200MHZ on water but when I went back to air couldn't stably run a 16X multi on air, my FX60 is essentially 2 FX55s, and on air I have them running a 15X Multi @ 3.0GHZ using 1.4V V-Core.