herr gunstig

Probably what you want is the one listed as channel pressure in the drop down for the table.

The old MainStage 3.3.2 had some options to filter midi messages out (such as aftertouch, pitchbend, etc.) The new MainStage has a list that allows you to filter out and/or transform any midi message you want, allowing you much more flexibility compared to before. However you need to have the midi get to the channel strip first which would involve either mapping some sort of mapping or checking the "send unassigned midi to all channel strips" option at concert level.

If you don't want a screen control you can also go to the assignments and mappings tab, click the gear menu and choose "new assignment" to create and screen control free assignment/mapping pair.

Stability/Reliability MainStage no longer quits unexpectedly: When an External Instrument slot name is shown and there are no inputs assigned. Sometimes when quitting after using the Jump to Next Marker mapping several times. When a new channel strip is set as default, and the Load Default option is enabled in the New Track sheet. Performance Faders now reliably remain active immediately after patch changes. Mixer Inputs for busses are now reliably maintained when loading saved patches. Plug-ins The Playback plug-in no longer sometimes cuts off the first quarter-second of an audio file. General Duplicate note off events are no longer sometimes sent from channel strips that have the No Transpose switch enabled. A sustain pedal off message is now sent to external MIDI instruments when the sustain pedal is released after changing patches. The Layer Bypass parameter state again returns to its saved state when selecting a different patch.

Did upgrading to MainStage 3.4.1 fix the problem?

See if changing this pref fixes it -- Preferences > Audio > Advanced Settings, change "Draw with OpenGL" to "Draw with Metal"

Has anyone tried out any of the drum/keyboard/audio performance views with the touch bar MacBook Pro yet?

I'm not sure where you're going wrong -- create an external instrument channel strip, go to the midi output tab, check "send midi file" and then choose a file.

If you can post your concert file somewhere maybe with some teamwork we can figure out a workaround.

I have used it with my EWI, most things work ok with breath remapped to control expression. Some instruments don't like the large and fast variations that BC can send, and then you get some audio distortion. I have had some good experiences with the Garritan sample products, which use Kontakt Player. While I know people don't consider them to be the best sounding, they are setup pretty well to handle performance via a wind controller when BC controls expression.

Dunno what the problem is with inserting mono jack into the headphone slot, but there are some combo audio + midi boxes you can get that are powered and will give you better quality audio than the headphone slot. Unfortunately everything I own has been discontinued so I don't really have recommendations. But probably the cheapest thing to do is that instead of plugging your computer in, you can probably run the midi interface through a powered usb hub and that would likely solve the power problem.

You can run midi monitor to see if your midisport is still working. Or try your axiom out. That way you can tell if its the midisport going bad... The other possibility is maybe if you are running off battery power and the midisport asks for too much power, then it gets disconnected by the operating system.

I think he was referring to the new midi message monitor (window > midi message monitor) which is an entirely new feature in MainStage 3. Since it displays a log of messages, you can actually see what is passing through -- the one in the toolbar just displayed the last message which was useless if messages were coming in quite fast.

Well you could click on each control and look at it, or look in the assignments and mappings table... or disable reset to save in the prefs and you will know if you have a mapping somewhere since it won't get reset after loading.

Do you have a parameter mapping to it -- if so, maybe its "saved value" is set to +6.0 (you can set the value through the parameter mapping inspector, or by saving the concert with the patch selected). You could also disable "reset to save" in the preferences under general > on patch change.