EZD2 (..or any multi-out drum kit)
1 The Preset has it's own custom mix (all out channel 1) and sounds good. ---> DRUMS [bus]
2 If all the drums then being (multi-out) to tracks and all the tracks sent to (1) stereo bus, should it not sound exactly the same as the preset? ---> DRUMS [bus] sounds like cardboard, even though all the reverb, Amb, etc. are on their own tracks, sent to 1 bus, no additional effects are added.
https://onedrive.live.com...amp;ithint=photo%2cjpg
 
Audio Comparison test ZIP
https://onedrive.live.com/redir?resid=E8C0550015EA481D!692&authkey=!AAX5m1e8gzv5qFg&ithint=file%2czip
 

I don't use EZD2 but I'm guessing that when the drums are routed to the master bus of the VSTi then they pass through some kind of on-board processing, whereas when you output the individual drums to their own outputs they bypass that processing. 

It could also do with the panning.  Stereo out might have the panning set, but when the synth outputs to multi with mono tracks, I think the panning is center for everything unless you set it in the output track (the overheads and/or room might be panned hard L/R.)  Also, almost always, when I use multi out the tracks are too hot and when summed by Sonar end up clipping.
 
I am not familiar with EZD2 but AD2 has a mixer section and you can output the processed stereo channel as well so it shouldn't be different

A Preset by it's very nature will be subject to all sorts of internal processing - EQ, Compression, Distortion, Panning, Reverb etc
 
When you start routing everything out to individual outputs you've lost all that processing so you'll have to replicate it inside Sonar.
 
This is certainly true with BFD and I suspect all the other major players.

Is there a pre-fader or post-fader option when sending out from the internal mixer? 
 
One of the reasons I ended up with the Steven Slate Drums is that the levels and processing didn't change when going to multi-out. I love Battery from NI, but it always gave me problems with multi-out.

I missed your picture the first time. It looks like your db levels aren't matching. Make sure that your stereo sends are in stereo, and your mono sends are in mono.
 

I use SD2 and have no change when using multi-out...or nothing that I have noticed.

I am thinking some kind of routing issue, as I have EXdrummer2 and Superior Drummer 2, amongst others, and have not noticed any change.

I will have a look back when I get home to see if I can help at all.

Thanks everyone for the helpful ideas. I don't have to use EZD, but I am looking to get a multi-out 1:1 with any of the the presets. I have access to: EZD2, SD, AD2
 

jb101When you start routing everything out to individual outputs you've lost all that processing so you'll have to replicate it inside Sonar.

I think this is true with EZD, I'll check the routing again and go through the suggestions, and see what works.
 

jb101I am thinking some kind of routing issue, as I have EXdrummer2 and Superior Drummer 2, among others, and have not noticed any change.

SuperiorDrummer and AddictiveDrums2,  have more options, (AD2 is actually good) so if you know for sure EZDrummer2 can be routed 1:1 please post an image or tutorial.

You may be getting phase issues between the vsti processed aux out(s) and the unprocessed kit piece direct outs.
 
Rocky