SoundCenter now detects the DSF Instrument Examples Pack.
 
Via a loosely-targeted Google search, I discovered a Steam message thread link with the solution. JoeStevensUS suggested moving the Cakewalk Sound Center folder from C:\Program Files (x86)\vstplugins to the hidden C:\ProgramData\Cakewalk folder. The extra Instruments appear in Sound Center as they should.

     http://steamcommunity.com/app/222710/discussions/0/846965056819493782/

However, I find this solution puzzling. I had the add-on working previously without having to merge the Sound Center folders. Then again, I don't remember if this was before my upgrade from Music Creator to Sonar.

In addition, missing Multisample errors were triggered by the instruments Lady Organ (Electronica), Deep Mind (Electronica), and Clay Tones (World).

Given these two issues, I'm guessing that the DSF Examples installation file may be flawed. However, the link above pointed me to the proper solution and what I thought was a tremendous issue seemed to be a mere files mismanagement.
 
Thanks to those who offered assistance here! :)