The plug-in is not added to
Preferences > MIDI > Devices. That is for connecting external hardware and software to MC6.
For the plug-in to work at all, I m pretty sure it will need to be configured as a synth. At least that is true for every other plug-in that uses MIDI I/O that I have used in Cakewalk software older than SONAR X3. This would include anything older than MC7 too.
I am not sure what you mean by "force MC6 to scan." Try running a VST reset from
Preferences > File > VST Settings. I have never had a plug-in completely disappear like you are describing. If you do manage to get the plug-in back, there is a registry settings which might need to be manually set.
Here is the process described for
MIDI-Guitar, a similar product. Note: These instructions are for SONAR X2 but both DAWs use the scan VST scanner.
I did not spend much time with MiGiC, I did encounter a couple of small issues with it and tried contacting the developer and never heard back. Since I already had MIDI-Guitar working I did not pursue MiGiC any further.