Hi Fred,
Just to illustrate that GPO and other software sound packages have their 'labour intensive' features, I have several organ packages, and they each have similiar problems:

(a) One organ packages requires a separate stave for each stop (almost impossible to use because of this)
(b) Another one requires notes be held down for the period that stops are drawn (ie each note on a separate channel indicates a stop is drawn, and if you want to have a stop drawn, then a certain note representing that stop is played - which can be for the whole piece). Again this is almost impossible to use, fortuantely there is a way around it, although it does impose some restrictions.
(c) Another organ package requires Modulator wheels be used for stop changes, each stop given a value of modulator wheel 81 to turn it on, and modulator wheel 80 to turn it off. Again, very hard to use, and the score is hard to read to see what is going on.

So don't feel too bad about the effort you need to use to drive GPO - and I'm sure sometime in the future interfaces to these things will be a lot better (at least I hope so).

Incidentally, I'm interested that it was necessary to do this with the GPO Jazz package, as I was wondering what they would do in this area.

Cheers ... Clyde