Sorry - I am a bit confused. It sounds like you are trying to mix the midi levels using the midi faders instead of the audio track faders.
1. Do you have each instrument in the Kontakt instance routed to its own Kontakt audio output channels?
2. Do you then have separate audio tracks inserted into your Sonar project and routed to pick up the separated output from each corresponding instrument's audio output from the Kontakt instance? (so that rather than all the instruments in the Kontakt instance using ST1 for audio output, there is one stereo output in the Kontakt instance for each instrument in the instance - ST1 ST2 ST3, etc., and separate audio tracks in the project assigned to each of the separate outputs for each instrument from the Kontakt instance?)
3. OR, are all your instruments in the Kontakt instance sharing a single ST1 audio output, and then you are attempting to control volume using the midi track faders for each of the instruments?
For MY projects, I load up 5-6 instruments into a single Kontakt instance, then I:
1. Go into the Instrument settings for each instrument in the instance (using the wrench icon for each of the instruments and then clicking on Instrument to get to those settings), and once there I make sure that there I remove the check for the parameter that is labelled something like Accept Standard CC 7 and CC 11 volume.... (or something like that I don't have Kontakt open at the moment).
2. Make sure the Output Section is open (there is a button at the top of the Kontakt instance for this), which opens up Kontakt's audio output channels, then click on the Batch Functions and click on the one that says something like 'Delete all output assignments and create one output channel for each loaded instrument'. Doing this gives each loaded instrument a separate stereo output channel from the Kontakt instance. (I also then rename each of the outputs to something shorter than what Kontakt names them - it tries to mash the preset name to be that output channel's name, and I prefer shorter names, like Piano, Organ, Violin, etc)
3. Insert a midi track for each loaded instrument (sounds like you have this done already), and set the output to go to the proper Kontakt instance. (I may havee 3-4 or more instances). I also then set the Midi output channel for each midi track to the correct midi channel assigned to each instrument in the instance. The midi output channel is set in each midi track, just below the FX Bin.
4. Insert a single stereo audio track or a left and right mono track, for each of the loaded instruments from the instance, and set the input for each track to the appropriate audio output from the instrument's output channel from the Kontakt instance. Because I renamed my output channels in the Kontakt instance, these are much easier to read in the drop-down presentation of outputs to pick from when assigning the audio track inputs.
5. Now, I control all volumes for all of the instruments from the Kontakt instance through a combination of the instrument's output from the Kontakt instance, the Gain knob for the audio track(s) for that instrument, and I generally set everything initially so that all instruments run at around -18 dB, and I leave the audio track faders at unity.
6. Once I begin mixing, I only have to adjust the faders for each track - or possibly also the Gain, but I NEVER have to mess with the midi faders whatsoever.
So - please run through how you are set up and how you are attempting to control things - THANKS. :)
Bob Bone