Many thanks for your informative reply, I did amend the ATC section of the MCE.ini as suggested and I noticed that now the key selected for the PF3 PTT press (INS) remains checked in PF3, so the tip was helpful, I also programmed in FSUIPC my Yoke Button 1 (PTT button for MCE) to be read as INS for PF3.
However, that does not solve the problem and this is what makes me nervous going ahead with the purchase because, in spite of all assurances I received that MCE and PF3 work together well, the demo does not, or perhaps I dont know how to make them work together?...
More confusing is the fact that when I press my (MCE) PTT, a PF3 pilot's voice comes on the frequency to request the clearance when I have followed the manual's instruction to deactivate the pilot's voice and the VCP is selected OFF in PF3 Options.
What works:
PF3 initiates the FSUIPC text window, the kneeboard gives the correct frequencies for the correct airport, ATIS is clear and correct
MCE is correctly set on PFE on the ATC UI page, it reads the correct flight plan, the CP is there and I can interact, but no static noise when I press my yoke button (although it is ON in the ini file), and no contact with ATC (clearance delivery) possible
I am afraid of having such issues after buying and I'd really like to make sure everything works as expected on my setup before making that move (which I'd like very much (I am one of the first FDC and S Combo customers for the old 742 so fully trust Dave's work)).
For your information I have used MCE for almost seven years now with FSX and FS9 ATC so I am confident it operates fine with my setup. If I can get these two software to cooperate then it's an instant buy, but for the moment after playing "guessing" for three hours, I am thoroughly lost and badly need help...