I split into separate tracks mainly because it keeps my workflow consistent between projects I record in the box myself and projects I mixed from outside sources.  Also, I can choose to apply the exact effect I want on the tracks instead of relying on XLNs effects.

I found it more cohesive and simpler to use 1 audio and split the midi in to separate tracks as well. I started doing this out of necessity, in the old days because those old computers didn't have enough horsepower to allow me to process every drum track without choking. It made more sense to me that its easier to deal with 1 plugin than 24 different drum tracks. I create a Drums folder for the split midi files and put them in there. This makes it very easy to edit velocities on just the kick, or just the snare, etc.
I also use the Cal for Split Notes To Tracks on single midi drum tracks. I split the drum track then identify and name what is on the individual tracks then they go in to the drum folder. It is a little more work but really saves time for micromanaging velocities on individual drums.
Of course, the computers we run now allows us to do whatever we like but old habits die hard!  Lol!
 

I split into separate tracks and bounce them dry, except for any "room" or "bleed" that makes the drums fit together. I then process the tracks individually in Sonar, and do further processing on a drum buss. In other words, I treat them as if I recorded them in a room. I find it much too difficult to predict how the FX is AD2 (or any synth) will fit when it comes time to actually mix the tracks.
 
Regards,
Dan

I fall firmly in the "mix it up" category.   My typical process is to start with a single instance, listen a hundred or so times, and decide whether it suits the song as-is.  I will often split out the kick and snare to separate audio tracks, and sometimes I'll also do the same with the toms.  And yet other times everything remains covered by that single instance.   I let my ears guide me down that path...
 
And like Jerry mentioned above, I usually replace individual kit pieces so rarely use a kit in its original form.  For example, on my current project I've replaced all of the cymbals and hihats and have tuned & tweaked the snare, but haven't touched the kick or toms (started with the Retroplex kit). 
 

With drum VST's in general, if it's "natural" drums like AD2 that have things like overheads and room mics as well as all of the other finely grained and complex mic options and such, I really feel like I get better results from leaving it all in the VST and outputting to a stereo track. Even if you're not entirely happy with the sound, then unless you're very experienced in mixing a drum kit from scratch then it's much easier to just tweak inside the VST using the preset as a starting off point. I've tried bringing everything out to separate tracks and it's almost never as good as the preset. 
 
However if it's electronic drums, like AD2's drum machine presets, or Battery, Geist, Tremor and the like, I much prefer to multi-out those and process them myself. No room mics involved, very simple sample based sound, and often involving kicks with much more bass content than usual. When it's a matter of taming very bass heavy sounds I much prefer to use my own trusty plugins rather than the on-board ones. 

I guess first we should know how someone uses AD2 as I can see from the comments there are a lot of different ways. For me, I wind up with individual midi tracks for snare, kick, and toms. But that's just because of the way I work and how I do it. 
 
I record a live acoustic kit, fully mic'd. Once I get the performance down and get the kit sounding like I want. Then I go back and use the kick, snare, and tom close mic'd tracks to trigger midi, copying the midi to individual tracks. 
 
I then use those tracks with AD2 and mix the AD2 sounds with my live acoustic kit. When I'm working to get the midi triggering right, I need the tracks separate so I can easily solo the real snare with the AD2 snare and make sure it's all correctly triggered. I always wind up with midi notes a bit off or some false triggering that I have to clean up. Same with all the tracks, so separating them out makes it easier for me.
 
As for the AD2 sounds, I use AD2 for the processing instead of printing tracks and working with the audio. But then I also have an audio track already from my acoustic recording to do that with. 
 
For the most part, I never use cymbals or hihats from AD2, I use the live overheads for those as they seem to glue everything together better. 
 
gabo
 
Check out our new album, Blue Sky, which was just released. All the tracks were done as above. Blue Sky is available on our bandcamp site and also spotify, itunes, amazon, youtube, and most other places. 
 

Thanks guys. These are all really great replies.

I think in my case I need to either decide to keep it all in AD2 and use a single stereo track or just send everything 100% dry and un-processed split into multiple tracks. Sending processed tracks into individual tracks is what is making it hard for me I think.

dcumpian
I split into separate tracks and bounce them dry, except for any "room" or "bleed" that makes the drums fit together. I then process the tracks individually in Sonar, and do further processing on a drum buss. In other words, I treat them as if I recorded them in a room. I find it much too difficult to predict how the FX is AD2 (or any synth) will fit when it comes time to actually mix the tracks.
 
Regards,
Dan

I use AD this way.

i've used AD for years, before sonar included it, and except for a couple of times I use the output as a stereo mix single track.  I send the mix to my 2 Buss and to an automated buss with a compressor and other magic stuff to spice up the mix in spots like loud parts of a mix.

I always use any drum lib as multi-out i.e. one audio track per kit piece. It usually takes some figuring out if you move e.g. from Kontakt to AD or likewise the first time, but once figured out I save a template and use that for loading.

This way you got way more control on the individual pieces (which is important especially for the very hot AD drum presets) plus you can still route the AD internal FX bus to a Sonar track and blend as you like.

The template is set up to include all drums and in case I work with a smaller kit I simply delete the unused tracks prior to mixing.