I took the suggestion of Mark and tried to add to the image some OIII I had (120m). I was not expecting much, since the brightness of the other data is overwhelming the OIII.. well, I was wrong
In fact the OIII is not contributing at all to the external side of the nebula but it is quite relevant in the core, in particular for all those "floating" gas and dust lanes. I don't actually believe that these details emits predominantly in the ionized Oxygen line, surely however this filter kill the Ha emission and permits a very high contrast of these details that I believe have a green-blue broadband emission.
Below is the version with OIII added:
http://www.glitteringlights.com/Images/deepsky/13667287_7Mtr58#!i=1735031770&k=xdQ 9RZs&lb=1&s=X3
Again, the view at full resolution ("O") permits to see these details at full glory. I am not sure which version is more pleasant in terms of overall color balance, for sure the new one has more details, so I believe I will keep only the latter. What is your thought?
Marco