I can't tell you guys how much I appreciate your help. Everything works perfectly. Sonar runs the pre-recorded MIDI track for the harmonies. An audio track is inserted to receive the harmonizer's incoming line signal. It's also routed to receive the MIDI notes. Now, I just have to hit RECORD on the harmonizer's track, step up to the mic, and start singing those fake, computer-generated harmonies.
 
Here's the corrected diagram, following your recommendations:
 

 

YAY - that's some GREAT news.
 
I REALLY like your diagrams, by the way.  What did you make them with?
 
Bob Bone
 

robert_e_boneI REALLY like your diagrams, by the way.  What did you make them with?

CorelDraw, the vector graphics program, not to be confused with CorelPaint. Student edition is quite a bit cheaper, and does pretty much the same as the "pro" version. LINK