How do I import third party software instruments into Garageband 10.0.3?

After attempting to select from my collection of third party software instruments, I find myself hard pressed to find any helpful information in this support community. The Edit tab in 6.0.5 has been replaced with a drop-down menu on the track header that lists "Plug-ins", but the section is greyed out. So I can only assume there is some sort of process I must follow to import my third party software instruments into Garageband 10.0.3. Since nothing related to this topic appears here, I suppose I'll have to bug Native Instruments.

Also, the piano roll edit window is either painfully slow, glitchy or completely unresponsive. It's as though 16GB of RAM isn't enough. Funny that the piano roll edits were smooth as glass using GB 6.0.5 and my TPSI worked seamlessly with that interface. And that was BEFORE upgrading from 8 to 16GB of RAM.

I've been a faithful Mac User since 1990, but between this kind of baloney and the crash-happy nature of Yosemite, all I can say is I am getting very disillusioned with Apple.