[al lkosmal]

Rutager,
The IACs I've installed and others that i've seen have all been plumbed into the same vacuum manifold as the ITBs.
I think that your experiment was a good one. If after adding all 6 ITB vacuum lines to the manifold, your map signal straightened out, it is likely due to having more signal averaging, resulting in a smoother signal. It also shows that your ITB balancing is not causing the bumpy MAP signal.
So, you could go back to your previous arrangement...if that was/is working for you...or continue with all 6 ITBs and the IAC plumbed to the vacuum manifold.......it is not clear if you have verified that your IAC is actually working. Based on your questions, you have not really tested or verified that.
I would recommend that you start there and.... at least that variable will be eliminated.
However, as I recommended from the start.....I would focus on getting your engine cold starting very well, so that it fires up with a single smooth pedal effort and will keep running with the throttle held open a bit until warm......this will verify that you have the cold start fueling correct, or close to correct....then I'd plumb the IAC in to emulate what you were doing with your foot.....I.E. adding cold start air, combined with cold start fuel.....