OK..... That's one heck of a deal.... wow....!
OK ... it's been a really long time since I installed my Sound center add on packs. And I don't remember the specifics.
However, the packs should install themselves where they are supposed to install. Accessing them is as simple as opening and running MC and install a soft synth choosing Cakewalk's Sound Center synth.
The sounds are all available in the GUI where you choose a sound. This aspect threw me too when I first installed the 2 sound packs I bought. I had to confirm that they were there by looking for the sounds contained in the packs, in the GUI. They show up in there with the 150 or so sounds that come with it as a default starter kit.
I did have some issues with the first kits not installing or showing up in the GUI. That was an issue that cake did acknowledge and worked with me on to fix. They had to do something to the kits and give me new links but that was a few years back so that aspect should not be the issue here. IIRC it was related to the Vista OS but cake solved it in a few days and it works fine.
In the GUI, where you choose instruments, with all the packs, you should have access to dozens of sounds in each category and sub category. Many of mine are empty. With all the packs, you should have many in each.
If you don't, do not uninstall and reinstall since that would not solve anything since it's not the problem. The program MC6 is installed correctly, but simply can not find the sounds.
Don't panic that you don't have it working yet. Not all installs go perfect. It took me 2 weeks just to figure out how to get sound out of the speakers. The folks here will do our best to help you get rolling.
Now that I understand the issue, I will look into my DAW.... because those sound files should show up in a specific folder on the machine. I don't have time right now to look it all up.... but I will check back later when I have the time.