Thanks for the extra detail Chris - I'm glad you got a new registration sorted.
For what it's worth (and I realise that you may not be able to load all the stops for this), if I had the medium edition, I'd probably use the Bourdon, Gamba and Celeste on the Recit as the accompaniment, and combine the Positif Cromorne with an 8' or 4' flute and the tremulant with the box half to fully closed for the solo. That would give you a degree of expression with a mild reed against a string accompaniment. I should say that I don't know the piece, but I've tried to imagine it arranged for organ from reading the score, so if the above wouldn't work, please ignore me
Likewise, for what it's worth, I do think that the Grande Orgue of the PAB is a little overpowered. Part of that is probably due to the dry acoustic - less blending between the divisions occurs than might if the organ were in a reverberant cathedral - and often the best way to use it in quiet registrations is as a "mixing pot" for the other divisions where the combination of a Recit registration with a Positif registration gives a contrasting, appropriately stronger registration without actually using any of the GO stops. Their power makes sense when you're playing with plenty drawn across the instrument - they add a breadth to the overall tone which you wouldn't get if they weren't big, fat and foundational, but - for instance - as I've said elsehwere, the GO Principal 8' really can't be used if you're playing less than
mf, which is very different from a Baroque instrument's Hauptwerk or even a Cathedral instrument's Great or Grande Orgue, where you would find at least some quiet, "accompanimental" stops.
Keep an eye on the forum over the next few days - I've heard a rumours relating to a project that might be of interest to you.
Adam.