According to the ORBX Central Manual, you should have created a Library (or several ones) in ORBX Central to install new products. At the same time, you cannot select a Library located inside the main sim directory (see Page 19 of the Manual).
I guess the only way to go is installing the new ORBX products outside the main sim directory.
Since this is a very good question I also have for myself, maybe someone from ORBX could chime in and explain better?.
Cheers, Ed