I bought platinum a couple weeks ago and just downloaded Cambridge and DimPro.
 
I now have Platinum applications in two separate places and DimPro data on my C drive.
Is it possible through Command Center to specify where installs are supposed to reside? Or
do I have to download an install package and run it offline?

The only installation control provided by the Control Center is on the settings page accessed by clicking the gear in the upper right of the Control Center UI. I expect you will need to run the installers by hand. No need to download them again, they are cached at the location specified on the settings page.

This should answer all your questions. http://forum.cakewalk.com...-a-Guide-m3183900.aspx