Andi - thanks, as always, for your help!
I'm using pages 4 and 5 of Optimizing… version 3.3, starting at 'More than one Vienna Ensemble'.
This is how I understand the process to work:
If you need to use instruments from two or more different VSL collections (e.g. Strings then Woodwinds), the best scenario is:
1 - assign channels (from channel 1 to a maximum possible channel 16) to each instrument in your score in the Sibelius (6, 7, 8) Play > Setup Manual Sound sets tab. By default these will be using MIDI Port 1 (one) in Vienna Ensemble Pro 6 (VEP 6)
2 - connect to the VEP 6 Instance by single-clicking on 'Show' in either the Active Devices tab or Manual Sound sets tab of Play > Setup
3 - for instruments in the other/second VSL collection add one or more new instance(s) of the Plug-in, 'Vienna Ensemble PRO Event Input' in the Active Devices tab of Play > Setup
4 - for each of these instruments likewise assign channels (also from channel 1 - do not continue from one greater than the highest channel number from the previous step - also to a maximum possible channel 16) to each such (second/new VSL collection) instrument in your score in the Sibelius (6, 7, 8) Play > Setup Manual Sound sets; these will use the next available MIDI Port… '2' if you did not change the Port of first VEP6 instance from the default '1'
5 - this time, single-click on 'Show' in either the Active Devices tab or Manual Sound sets tab of Play > Setup to Assign these to the relevant instance of VEP6 using the Assign window (as in the existing screenshot)
6 - be sure to select the new MIDI port (probably '2', see step 2, above) in that window, at its top right. Nothing in the Sibelius Manual Sound sets tab of Play > Setup needs to be changed to reflect the use of this (new/second) MIDI port.
I found that sometimes this is is a bit hit and miss and requires me to Cancel to force the necessary Assign box to appear; I was then a little confused about the difference between the 'ASSIGN' button under the blue bar (reads '(unpreserved)' in that same screenshot) vs the 'Assign' legend bottom left after you have clicked on that first button.
I'd also find a table of some sort directing the user as to which settings in each instrument for the 'Master', 'Bus', 'All/nn' etc. I usually get there. But by trial ane error.
I believe the procedure differs with Vienna Ensemble (not Pro).
Have I got most of this right, Andi?
I hope some of it might be useful. If not, just discard. It reflects the step-by-step way in which I think. Whereas Optimizing… is very good at describing the concepts behind the way the software has been designed and built.
Not a single word of criticism here, Andi. I love (using) this product. But I know it can be confusing at times - because of its richness and power.
Thanks for listening!