If you look here:

https://www.presonus.com/products/Studi ... e-versions

You will see exactly what is available only in Prime. Only Presence XT is available as a virtual instrument. Also only two Soundsets are available for it.

1 Prime Selection Loops and Sounds
2 Studio One Instruments Vol 1

I also find a good way to do it as well is to download the Soundsets in question first. Then open Studio One and when you get to the start page, do not do anything at this point.

In the Options/Preferences under Locations/Soundsets you will see here where it is going to install them. If you happy to allow them to go there just leave that and drag the install file onto the start page. It will install there.

If you want a Soundset to be installed elsewhere e.g. an external or another drive etc then remove the location that is indicated. Then look at the window that says Install To. Over on the very far right is a little square with 3 dots in it. Click on this and navigate to your preferred location. It will then appear in the area below. Then drag the install file onto the start page.

if you do install elsewhere Presence XT will automatically know where to look.

Prime is free so you cannot expect to have access to a huge number of Soundsets. Artist allows you 6 and pro lets you have all of them.