I'd be surprised. The Honda manual is the Honda manual, it doesn't lie, it has the same part number for all '21 looms.
As Monkey says the Mmax box is a waste of time as it only does the pgm splice which is just one wire anyway. The box also came with jet settings and a free flow filter, were they done too?
Any engines power is directly related to the amount of mixture it can get into the cylinder and neither the mmax box or the wire splice change this at all, all the wires splices (there are 2 of them really) do is give your bike the potential to produce power, if no more fuel and/or air is getting in (presuming the jetting was optimal anyway) then the effect is likely to be minimal if you're lucky and seizure if not
_________________
Please do not PM me technical questions, if you can't find it on the Forum start a thread