I have Helm in my fx menus. Can I drag it into the Instrument choice menu. Helm seems to have a much better fidelity than some of the Apple instrument sounds. It has a Virt. keyboard on the bottom of its screen, I assume that will work ok...

If Helm is showing up in the FX menus in GB then you must have the AU version correctly installed (in Library/Audio/Plug-Ins/Components); with an Instrument track selected it should appear in the Smart Controls Edit pane Plug-in area (on the lower left), selectable form the top insert slot (under the AU Instruments submenu)..