from what you just said id'e say its not the mdex, its you, by the sounds of it you're not beatmatchning long enough. you may be only out by 1 bpm or so? and you might not notice that after 4 bars? then just bang it in anyway but after 16 bars or so, that 1bpm out is now 4 or 5? also saying moving the pitch up 1 notch is faster for some tracks than others? yeh duh moving the pitch changes the percentage. so on a track thats 125 bpm moving it plus 1% (or one notch) it is now at 126.25 bpm (1.25 bpm(1%) gain) and a track at 140 at +1% would be a gain of 1.4 bpm (141.4) so moving the pitch varies on the original bpm of the song, not just moving pitch "notch" = 1bpm or whatever so in conclusion, you may be not moving the pitch enough for different track to make the bpm differences the same? and therefore your tracks are going out of "sync after a few bars"? sorry for the rant, hope this helps?