See this thread for more thoughts:
http://forum.cakewalk.com/Drum-Replacer-Snare-hits-louder-at-different-times-when-using-a-static-sample-m3298373.aspx IIRC, to flatten the dynamics, you want to set the control to 100%, not 0.
But perhaps more importantly, it doesn't make much sense to use Drum Replacer on a synth drum track except maybe for experimental/testing purposes. If the track originally came from a synth, that means you either have the MIDI already, or can extract the pattern from the synth to a track to use with a drum sample player like Session Drummer or simply a another synth that has the sound you want.
Working with the MIDI and sample player will give you more control over timing and dynamics, and the ability to easily change the pattern.