I  would second Beepster's recommendation to pull down the output levels of channels in AD2's GUI - preferable to adjusting Gain in SONAR in my view.
 
Lowering MIDI velocity is akin to having the drummer play more softly. You'll be hearing only lower velocity samples which may not be what you want, depending on the song. Usually some combination of both audio output level and velocity tweaking are needed to get the right sound, but you want to start by making sure the levels are reasonable when the kit is being played at full velocity.

As far as velocities go, it makes sense to me to use the ranges found in the AD libs when creating your own patterns.

BobF
As far as velocities go, it makes sense to me to use the ranges found in the AD libs when creating your own patterns.

+1   I find most of AD's included MIDI clips have an optimal velocity range for the samples, a fairly "natural" feel to them with some velocity headroom to spare if and when needed.