The file I used is: SBLWMEDrv.exe
This file is on the URL page that you referenced, but since there are other files on that page I just wanted to be sure that this was the file you downloaded.
Also, you might need to reinstall Sonar to get it to recognize the new WDM drivers (there's probably a way to do this without reinstalling, but I'm not sure how). Make sure you have installed the WDM drivers for both SBLive and Delta before you do this. It should then recognize both cards.
The WDM files are better with Sonar for getting reduced latency. If you want better latency, then WDM is the way to go. Otherwise I don't think you'll have any problems with MME drivers.
The clicks and pops you got were possibly the result of having your latency set too low. In the Sonar Options -> Audio menu you will find settings for mixing latency. Try pushing the slider for buffer size further to the right (safe) and see if that gets rid of it. You can also increase the number of buffers just above this. If they are currently at 2, you might try going to 4.