A friend of a friend has a Terratec card with 4in/4out - there was nothing he had to do under Sonar to get it to address all of these correctly.
Check under OPTIONS-AUDIO-DRIVERS and make sure that all 16in/outs are selected for use with Sonar.
If that doesn't work, I would backup and delete your AUD.INI file, re-open Sonar and let it re-profile the Terratec card.
If that doesn't work, I would make sure you have the latest drivers for the Terratec card.
If that doesn't work, I would try and see if it worked using the older MME driver model.
Based upon that information, I would then make life a living hell for either Terratec, (if I suspected the drivers), or Cakewalk, (if I suspected the application), until they told me how to fix it.
Given the fact that ASIO did the same thing as WDM, I would say you haven't turned all the devices on, (as per my first step). If that isn't the case, I would be starting to look at other demo programs to see if they showed all the outputs correctly. If they also didn't see the outputs then it may be indicative of a hardware conflict.
Ciao,
Q.