Student453440 wrote: (Quote) Can you go over the process for bringing in free plug in sounds especially synths and how you get them to show up in the instrument choice screen...? (Unquote) 3rd-Party AU (AudioUnit) instruments would be installed in the usual location (Library/Audio/Plug-Ins/Components), and then they should appear in the Smart Controls (Track) Edit panel (see screenshot below). If you find or create a sound you like, you can save it as a GB Patch via the Save button at the bottom of the Library panel, and then that Patch will appear in the Library under User Patches.

I downloaded the ReverbSolo fx and did finally see it in the the fx list..I also tried a new distortion on the Apple list there. But when I replayed a cycle of my song somehow just playing with those fx had made the volume on track2 almost silent. That was with both of those new fx turned off. I closed the file and reloaded it and it was back to normal. What might have happened there??

If you just closed/reopened the file without doing anything else to it and that got it back to normal, then it was most likely just a (hopefully one-time) glitch; worst-case scenario would be some kind of incompatibility with the newly-installed FX. If the problem happens again it might be worth it to de-instantiate that effect (remove it from the slot, not just bypass it) and maybe work without it for a while—if the problem goes away then it could be an issue with that particular piece of software * (and welcome to the world of 3rd-party s/w issues!). ;-) * I don't recall what your system spec is but on the Reverb download page for Reverb SOLO it only specs compatibility through macOS 10.12, FWIW..