Hi Rachel and thanks for your quick response.

I can get to the RT picker - either using the icon you described, or by R click on the track and select "add/remove real tracks". In the picker dialogue box I can select the track (ie mixing track) I want to change, and then highlite the new choice - but then what? Do I just close, or do I have to hit the "generate track" button?

Either way, back in the main window if I select the changed track eg Strings, the info box top left shows the new choice (and very confusingly in the drop down beneath the original instrument) but I dont hear anything play. this happens even if I did do the generate track button.

cheers, Tom