Following the link to Sonar Platinum on the My Products (and landing on the page for Platinum) on the right is a list of downloads. One of those is Platinum Core Plugins.
 
I'm assuming the downloadable installer is provided because they plugins aren't handled by C3. Is that the case?
 
Which plugins are included in this installer?

The Command Center downloads and runs the Platinum Core Plugins installer as part of the SONAR Platinum line item. When running the SONAR Platinum update in the Command Center notice the number of files downloading. The installer is also stored in the Command Center download cache with the rest of the installers. When using the Command Center there is no need to download anything directly from the store account for the new SONAR.
 
I have no details about the contents of the installer.

Thanks, scook. The confusion has lifted from my brain. ;)