Wow. Life sounds hard for your family and your son. A few questions for you:
1) can you outline a pattern for the current behavior, when did problems start appearing, what the evolution was and how/when you got the diagnosis (ADHD/dyslexia)? Who did you see, when (how old was he), and did you get all the labels at the same time? Do you have detailed scores for the WISC-IV (all domains and subscores)?
2) what's going on at school? What grade is he in? CE1/2nd grade? What month was he born in (is he young for that grade?)? Is he showing the same behavior issues there? How are the teachers handling his differences -- both the giftedness and the learning disabilities? If you are about to get an AVS (note to other participants: special assistant = 1:1 aide within a mainstream classroom) I am guessing the situation is not good there, but... more details?
3) How does he do with other kids? Does he have siblings? Friends? At school? Outside of school?
4) You said you went through 3 dyslexia specialists. What didn't work with the previous ones, what works with this one?
I don't know if it has been recommended yet but if you can read it without spending months laboring over the translations try ordering this book:
http://www.amazon.com/Misdiagnosis-Diagnoses-Gifted-Children-Adults/dp/0910707677. It goes through basically all the DSM-IV labels (including ADHD and ASD, because the behaviors you describe don't scream ADHD to me, but then I am not a specialist) and tries to distinguish gifted symptoms from other symptoms.
Re. reading, how did he react to the higher level texts you reqd to him? Did you try books on tape? Books that are appropriate for his probably low reading level might be excruciatingly boring to him.
And I would definitely talk with him about his exceptionalities -- if only to say that you understand how frustrating it can be to have so many ideas and such a hard time getting them out.
Lastly... Your written English is good enough, but I have no idea how hard it is for you to type this all out (and/or read other people's posts). I'd rather keep this discussion going in English, because you will get more useful feedback from other people with better knowledge of your issues this way, mais je peux parfaitement continuer la conversation en français ou clarifier des traductions si nécessaire.
