Its either what Fasterbikeboy said about the driver mode using WDM as far as mapping goes or your mixer/interface is defective
 
Cj

Karl, Cj - Please read my last post (#9) above.
As I stated initially, I've had the system since February of this year and with the learning curve (and limited time - I don't do this stuff full time) it took me awhile to get this far. My first project did not require more than 5 channels, so the boards' channels 9-12 may have been defective from the start. It's only been with this new project I've begun that I needed the upper channels on the board and that I've noticed a problem. As new as I am to DAWs in general, I thought for sure I had something not set right within Sonar.  
I'll go ahead with my recording today, using channels 1-8 on my board and if I need extra inputs I'll make use of channels 13-16.
 
Thanks so much for your help. I'll need to see if I can somehow get in touch with Allen and Heath. When the Zed first shipped in 2007(?), there was a grounding issue withing the circuitry that they were happy to explain and allow the owner to fix. I'm hopeful it's something simple (perhaps a connector feeding the 4 disfunctional channels has come loose).
 
 

Check the ZED Dice Control Panel settings. Each of the channels are mono so if you have it set in stereo mode then it pairs the inputs like this: 
Stereo 1 = 1L/2R
Stereo 2 = 3L/4R
Stereo 3 = 5L/6R
and so on. 

daveny5
Check the ZED Dice Control Panel settings. Each of the channels are mono so if you have it set in stereo mode then it pairs the inputs like this: 
Stereo 1 = 1L/2R
Stereo 2 = 3L/4R
Stereo 3 = 5L/6R
and so on. 

Thanks, Dave, but wouldn't such a setting be universal to all channels on the board? Check out my posts above - channels 1-8 work as they should (I'm recording with those channels right now). I get no signal to pass on channels 9-12 on my Zed. Channels 13-16 seem to work fine.
 
I did check my DICE settings as you suggested. The only place I see 'Stereo' set is on the WDM tab for 'Speaker Setup'. The word 'stereo' is not found on any other tab in the DICE control panel as I have it configured right now.
 
Thanks for your help.

You did check 9-12 through headphones on the ZED, right. So its just not sending 9-12 to Sonar? 
 

Yes, Dave - thank you. I did insert a mic on those channel strips and I'm getting a signal in my headphones when the signal is routed through the analog path to the board's stereo out.
 
Another thing to consider: I recorded a signal onto channel 3 of Sonar, through channel 3 of the Zed. I clicked and dragged the clip to channel 10 in Sonar (this is one of the non-responsive channels on my Zed, remember). The wave form is there on Sonar's channel 10, just as though I recorded it there originally. If I try to play it back, however, it only becomes audible if I press a button on the Zed that monitors the Master of my project in Sonar. It doesn't mix in with the Zed's Main Mix L-R that all my other recorded tracks do (on channels 1-8 in Sonar, and coming down their respective channel strips on the Zed.
 
There is another button on the Zed that will actually route the Digital Master onto the buss for the board's Main L-R, and it'll do that, but the signal on channel 10 in Sonar does not get to the #10 fader on the Zed and as a confirmation of that, there is no signal when Pre Fade Listen is selected.)

WHEW!! Solved this one and it was the Zed, not a setting in Sonar.
I took the back cover off of the board and had a look around. I could immediately see that the 2 sets of 8 channels were grouped together via circuit boards, and further, the 2 sets of 4 within the group of 8 each had a connector. I was looking at the back side of a circuit board, but I could see that the connector common to channels 9-12 appeared to not be seated in its mate on the circuit board. I touched it lightly and it came right out of its socket!
I carefully plugged the connector back in and got things up and running - everything now works as it should.
Thanks for giving this problem some thought and providing me with some ideas to troubleshoot with.

Good catch!