Many Instruments Make no Sound

Some Synth sounds work but most do not. In a track I can select, say Alchemy or ES1 and try a hundred different presets and the vast majority will not work, but a few work just as you'd expect. Some of the ones that generate sound, however, seem monophonic (only play one note no matter which key you're playing) even though these sounds are polyphonic and work perfectly in Logic X.

• I downloaded and installed all sounds: MainStage menu | Sound Library | Download All Available Sounds.

  Downloaded 18 GB - restarted, didn't work. Restarted macbook, didn't work

• In Sound Library Manager:
  • All Sounds are installed
  • Tried to re-install Alchemy - did this but again it did not work

Surely somebody has had this problem?

My controller works with everything in Logic X, as it has for years. I am not getting the same sounds in Mainstage. For example, the Alchemy synth which has over 3,000 sounda. In Logic, perfect, in Mainstage, not even a fraction of the sounds are playing. Spent hours rechecking settings, re-installing, un-installing... Ready to go back to Ableton.

Focusing only on getting Alchemy to work in Mainstage, I uninstalled/reinstalled Mainstage again but of course this did not help. I'm out of ideas. Why do all of the Alchemy sounds work in Logic X but almost none Mainstage? Again, a small handful of sounds will create audible noises but they don't function properly as they might play one note and only one note (regardless of the key you're pressing on the midi controller) but sound nothing like they do in Logic. The vast majority of sounds do nothing and a few others still might show volume output on track mains, but nothing is actually coming through the speakers.

Perhaps I need to physically delete the Alchemy files (where ever they are) and reinstall them somehow?

Also, I have MIDI Mono Mode set to "off".