The proper way to install your legacy Sonar products and Cakewalk by Bandlab together:
1. First install your Sonar products in the order of the versions that you wish to have installed. You can use any of your installer files/disks and serials, or the Cakewalk Command Center for connected products, just like you always have.
2. Install BandLab Assistant to get Cakewalk by BandLab. Cakewalk will scan and use any plugins you have already installed on your PC, but the installer itself only comes with minimal plugins so you should have already installed everything else you will need.
BandLab Assistant only downloads and updates the Cakewalk by BandLab program.
You will need to rely on the old legacy methods for installing any available updates to legacy Cakewalk products. BandLab has not released any updates other than the core DAW so far, and no specific announcements have been made regarding future plans for other products.