Here's a tip: once you get it sorted, save the SD setup as a preset. It'll save a lot of manual finagling in future projects. Track templates take it one step further. Because SD is my go-to drum machine, it's included in my standard project template so it's just there when I start a new project. Later on, when I've got SD dialed in for a particular song, I'll save a preset with the name of the song I used it in, so that later on I can browse presets knowing kind of what they'll sound like.
My standard setup uses 5 busses within SD's mixer: kick and sub-kick to channel 1, snare top/bottom/compressed to channel 2, toms to channel 3, overheads to channel 4 and room mics to channel 5. I then mute any mics that aren't being used, such as the sub-kick or far room mic.
Each SD mixer channel is then routed to its own audio track, so altogether there'll be 5 audio + one MIDI track. These all go into a track folder for tidiness. SD's busses are all stereo, so if you want mono out just use one side of the output, e.g. output 1 only instead of outputs 1&2. I do this for both kick and snare (so I'm using outputs 1 and 3, respectively).
While I'm at it, I'll throw out a few other random SD tips...
Select "16-bit samples". They'll load faster and take up half the RAM. If you like, you can switch to 24-bit before your final export, but it won't change how they sound.
Start your mix with no room mics or bleed. It'll make your mix go quicker and use less CPU and RAM, allowing lower latencies while tracking. When adding bleed in, reduce the amount for kick, hi-hat and toms if you have a dense, busy mix, to improve clarity.
The built-in transient shaper is a hidden gem. Give 1-2dB attack boost on kick and/or snare.
The built-in compressor is a bit heavy-handed for my taste, but used on overheads can give you that white-noise cymbal wash of classic Beatles recordings. Also try compressing just the top or just the bottom snare mics for a wider range of snare sounds.
200Hz is the magic band for EQing snare. Boost it for a fat 80's sound, lower it for a crisper metal sound. Speaking of metal, the built-in equalizer works great for bringing up the kick beater for fast kick hits. For a fatter, deeper kick lower the velocity values in the MIDI track and turn up the volume. This is a good trick for big symphonic hits, too: very low velocities and crank the volume.
Use the envelope controls on a per-instrument basis to chop off ring times for toms. In heavier genres, you usually want the toms to sound tight, without a lot of ring to them. Once you do that you can boost the low end using the built-in EQ for a nice thick tom sound. The release adjustment is very touchy, so tweak it with the instrument soloed.
If RAM is getting tight (not a problem for everybody, but for me it is), select the "Cache" option. This will cause only those samples that are used to be loaded into memory, which will cut your memory usage way down. You do have to play the song all the way through one time to load the samples, though.
Forget the factory-supplied presets and don't get suckered into buying the add-on presets. They are all designed to make drum solos sound great, not to fit the drums into a mix. Their only value is to instruct you on how to use the built-in effects, which the presets tend to over-use. Put your EQ on the busses first, and only add it to individual instruments on as as-needed basis. There is no need to EQ every microphone.
The built-in effects are quite good, even if the UIs are a bit cramped. If you use them well, no other effects will be needed on the drum bus. I used to add a limiter and/or EQ there, but nowadays my drum busses are completely naked. The only things missing from the built-in effects suite are reverb and distortion. With the far room mics, reverb isn't needed with SD2 except for special effects. For distortion, I like to use a separate bus so I can automate how much there is. Distortion is especially good on snare, a little less on toms. My favorite distortion plugin for drums is Redopter from d16.
The only limitation for me with SD2 is lack of a full-sounding deep kick. The sub-kick doesn't do it for me, so I often layer a synth over the kick to give it some deep thump. Any synth can do it, but I like Zebra. SD2 also lacks basic percussion instruments, such as mallet cymbal rolls, shakers and tambourines, so Jamstix and Kontakt are frequent collaborators on drum tracks. Jamstix's percussion pack has a nice assortment of tambourines and shakers.
Part of my standard preset is pulling the toms in toward the center. I like them to have more natural-sounding panning. The default has them spread hard-left to hard-right. Those itty-bitty pan sliders are a pain, all the more reason to get them set once and save as a preset.
OK, enough rambling. I forgot what the original question was...anyhow, it's time for breakfast.