Thanks.
Do I need VE Pro for that? I have a licence for VE Pro 5 which I used back in the days when I needed multiple networked computers to run all this stuff. But I stopped using it because of the lack of high DPI support, and the normal VE Pro seems to do everything I need nowadays since I can run everything on a single computer. (Or could with VI, anyway!)
Individually disabling every unwanted channel (when I have around 100 channels over 7 instances) would be something of a pain (even with MIDI commands), but it might be manageable if I could disable entire sections (e.g. choir) when I'm not using them. From what I can see, simply disabling the Master Bus channel has the effect of disabling all the channels that are routed through it, but not knowing exactly what's going on behind the scenes, it's hard to be sure if this is an approach that would work. After all, it doesn't make much sense that disabling a channel reduces CPU requirement, when that channel isn't being used in the score in the first place!
Mike