Hi NewIgnis,
First a big thank you for your insights and all the help you’re offering to newbies like me.
Among other precious sources of information I read your Adding patch parsing to a preset. Step by step thread which was very valuable for getting started. However I guess I read it a bit too fast… 
I fixed it and it works obviously, and I don’t understand how I got it to work in the first place.
But I’m still having a problem with the preset web editor response display.
On another preset I’m currently working on (Cheetah MS6), I get the response displayed only with zeros, which doesn’t correspond to the sysex response I’m getting back.
For example:
Whereas the sysex request/response are the following:
It always stays all filled with zeros even when i change patches on my MS6 and trig another request, but the changes in the bits between the different requests/responses are still being marked in green. Very strange… What have I done wrong this time ?
Again, many thanks for the help !