I have not tried the x esc's but have had a long relationship with my mmp and its been great. Two question for you. Did you double check that the sensor harness is plugged in correctly on the esc ? I personally disagree with using an adapter like they do but I'm just a end user. Did you set it for senored only or did you set it for smart sense ? Either should work but....... I would assume that it is set for non sensored from the factory since you have to buy the sensor harness adapter seperate. 2s to 6s doesn't matter I run my mmp/3800 combo on 2s up to 4s and it does not cog but I've set timing at lowest and power setting to full so it will pull all the power it wants or needs from the battery.