Update and success.
Strange things were happening. First, I flashed the updated FW, but still impossible to link.
So, I decided to roll back the mod and install the original antenna. In order to give it away to some interested party and keep the mod kit.
Just before closing the case, I tested it out again and ... it linked! (yes, the RC works w/o the joysticks connected and when open) This made me wonder.
Now, I reinstalled the mod kit (but with another set of SP-SMA plugs as I have two sets). And with two pigtail antennas, it still worked. RC closed, tested again, everything works as it should (test flight ok). Other than assuming that one or both RP-SMA plugs have been defect, I have no explaination for this.
I am happy I don't have to aquire another RC (although I found one new at 130€ which is pretty bargain). and that I am through this.
Some details about the mod:
I have both the "Clean Install Kit" and the "Itelite Nanosync for Mavic Kit". I used the Clean Install Kit (but with the RP-SMA plugs from the Itelite), i.e., I did NOT install the bracket for the Nanosync antenna. Reason is that with the bracket installed, other antenna with RP-SMA connectors may not fit anymore (too tight). One can, however just shift the Nanosync bracket over the SMA connectors (w/o screwing as it fits tight anyway) and still use the Nanosync. As I am not sure yet how much I am going to like the Nanosync, I prefer it this way. It is what Ender did too
@xtro83 the mod may not alter the ac. However, the better antenna does still improve the transmission from the ac, not just to it. However, any additional amp won't help the transmission from the ac. The mod though is amp free.