One volume fits all? No it doesn't...
I program Addictive Drums note by note by note. You have 126 different "volumes" to choose from.
You have to work out whether a snare hit (and it's always a fucking snare) at 85 sounds better than a hit a 110 because they use different samples and they sound different.... a matter of working out what's best for the song, tonally.
The same thing a real drummer would do if they tracked a tune and went back and thought "you know, a lighter touch on the snare might work better in this song..." Except all we MIDI drumbers have to do is turn the "volume" down to get a different sample.
I get all this, but this has nothing to do with volume, just sample tone, and once you work out your tone, and use both your DAW mixer and the (assumption) EZ Drummer interface mixer mix it into your music, then it just becomes part of everything else and shouldn't really be that much a separate issue in the quest for overall volume in the final mix unless you've done some really crazy shit in your mixing...
So, I don't think anyone here is sure of what your problem is... hence we say "post a sample" so we can help...