I’ve spent a few days troubleshooting the process of interfacing my Roland TD-4 e-kit with SD2 inside Sonar. My USB interface is a Roland Quad Capture, btw.  I think my buffer settings are pretty good. I have the e-kit connected via MIDI to Sonar’s SD, and after some tweaking between the software and the drum pads themselves, everything seems fairly copasetic; however, my question really involves the “Drum Mapping” portion under “Preferences.” There are a ton of preset options—some appear to be hardware based and some appear to be software based—but none of them include the Roland TD-4. What exactly does this do, and what should I use for the preset? Currently, I have SD2 set as the default.  
 
Also, I am still experiencing a little latency, and I’m unable to pin down that perfect balance of unnoticeable latency without the clicks and pops.
 
 
Any suggestions for the above or simply anything that would make the MIDI interface process easier would be greatly appreciated.
 
 Best regards,
 
Chris

Welcome to the forum.
Drum maps are just lists of all the banks and patches a device or soft synth has to make it easier to play with SONAR. You'll see their drum names in the Piano Roll view and the correct sound will play when you enter or record a note in SONAR.
If you select the Alesis SR-16 Acid kit drum map and don't have an Alesis SR-16 connected, you might hear something, but it won't be the SR-16 sounds.
Check out the Roland web site; they may have a drum map for the TD-4.
 
What are your settings under preferences now?What Driver Mode are you using?
What's your operating system and is it 64-bit? Which SONAR program are you running? Have you checked out the Troubleshooting section of the Help files? And the Improving Audio Performance chapter? Lots of things you can try, just make sure that no other programs are running, especially virus scans (get off the internet and disable the modem first).
Turn off Microsoft System Sounds.
Turn off any power-management schemes that may be on by default.
Turn off the screen saver and wallpaper.
 
 
 
 

Since you are triggering SD2, using the SD2 map, as you are, is correct.
The map is for where you are going, not where you are coming from (ie. destination, not source).
If you were sending the output of the MIDI track to the TD-4, then you would map to the TD-4.
However, I don't believe a generic TD-4 map would be meaningful, as you have numerous sounds to choose from.
In Greg's example, The Acid drum kit is a specific set in the Alesis SR-16 library. The kit is predetermined by the module, and the map is pretty straightforward.
Does that make sense?
As for click/pops vs latency, are you using the Quad exclusively?
Don't send the output to your built-in sound card. Ideally, the ASIO drivers for the Quad should give you the best latency.