I've got hold of midi monitor, and have run Massive standalone, then played it using MIDI output 1 from the 'harp. Is there a way to get MIDImonitor to capture the MIDI flow between EigenD and an AU that it is itself hosting? Or is it all internal to EigenD at that point?
Anyway, in the standalone configuration I notice several things that are different, probably because of the nature of the setups and the differences inside the midi outputs and the AU host. In standalone, all the controllers seem to be in some kind of absolute mode, whereby they snap to 0 when you start to press a key, or touch the strip controller. This overrides the panel control in massive such that the dial jumps to the minimum position and then follows the key movement. When you release the key the dial stays in the last position it was in, and then only jumps back to 0 at the next keypress.
In AU configuration, with the key axes and strip controller working through the parameter matrix, I observe a relative behaviour, in which pressing the key doesn't move the dial until you push it out of the centre position, even if the dial is not initially at 0. Pushing the keys will modify the dial without a jump to 0. Bending the keys left seems also to be able to produce negative values, where the dial will be drawn incorrectly (I've seen this with faders in Omnisphere too come to think of it wehre negative values causes the fader knob to be drawn a long distance away from the track). When you release the key the dial makes an attempt to return to the starting position, presumably because as the key springs back it sends further messages (although interestingly the absolute mode seems not to do this, ie the key up comes before the key springs back fully).
It's almost as if the system is entirely relative and is relying on the 'bend right' messages exactly matching up with the 'bend left' messages to get back to relative 0.
I can see both the absolute and relative modes being useful, and in fact the relative one in particular makes this patch awesome to play - you can fade in a brighter tone with yaw, affect timbre and volume with velocity, optionally fade in a huge sounding filter swell with pressure, and then move the cutoff around with the strip controllers. The drifting controls spoil the effect by moving the home position of each of these parameters, and means the sound becomes more and more extreme as the controls drift.