The bottom line is that has been one of Logic's most glaring "missing features" for years, in my book.
The problem stems from the fact that Logic can't separate the channels (or 'channelize') the volume and pan controls for the individual MIDI channels of a multitimbral virtual instrument. By contrast, Logic has no problem doing this with external MIDI modules. And other DAW's - I'm told - have no problem separating the volume commands for individual channels of a virtual instrument. But Logic "Pro" still can not.
So you have to set up a bunch of virtual 'aux' channels, route the various VI channels to the separate AUX's, then control or automate the volume of those aux channels separately from the 'master' VI. Personally I can't believe people don't complain more about what a needlessly awkward workaround this is, all to achieve the same basic functionality we've had in MIDI for almost 20 years now ⚠.
But that's the way it's always been done on Logic, and from the looks of it, there's no reason to expect it to change anytime soon.
Search the forums (or Kontakt's manual or Garritan's site) for info on how to set up numerous auxiliary outs, and that should get you going. There are also numerous tutorials and how-to's on this forum and others, which you can probably find if you search "multitimbral aux".
Lastly, some folks resort to automating volumes within the plugins, ie. adjusting the channel volume sliders on Kontakt's internal mixer while the sequence runs, then editing that automation later in Logic. Again, I think it's a kludgey workaround. But Kludgey Workarounds have always been a big part of the Logic Pro 'experience!'
Enjoy.
