Yamaha DTXpress/DTXplorer/DTXtreme

I had the same problem with my kick pedal registering double hits.  I 
determined that the kick tower and settings were fine but that the 
beater was rebounding and causing the double hits.  The solutions I 
used were as follows:

1.  Instead of playing flatfooted (heal down), I switched to heal up 
(toe down) and had a much easier time controlling the rebound of the 
beater.  This way it's easier to drive the beater to the kick tower 
trigger with more force.

2.  I bought a better pedal.  I had been using an entry-level Yamaha 
and switched to a Pearl PowerShifter Eliminator which is extremely 
stable and very adjustable to suit different playing styles, etc.

Hope this helps.