It sounds like you will have a lot of information next friday. Basically, when you do see the psychiatrist, s/he will review the information and agree or disagree with the psychologist's findings. Most of the time they agree with the psychologist because the evaluation is very comprehensive.
I think it's great you are doing this when he is so young. It will make it a lot easier to meet his educational needs with this information. Whatever his dx ends up being (if any), I can mail you a great deal of information related to that dx and the educational system in general.
We have talked about this before regarding my son. If your son ends up having Aspergers then I have some great information for you provided by the speech pathologist at my school. She is the "asperger and autism" guru of the school district and I highly respect her.
When the psychologist goes over the information, it may be a little daunting. S/he may discuss all these different tests and subtests and may go over standard scores. If it becomes confusing, just pm me and I will go over it more with you.
Even if you are expecting a specific dx, if that dx is confirmed for you don't be surprised if you still feel a flood of emotions. The emotions could occur for a variety of reasons such as confirmation, worry, confusion, relief, etc. I experienced that personally and I had no doubt in my mind what the clinical psychologist was going to tell me. Honestly, I wasn't expecting to have so many emotions when we met with the clinical psych. I already knew the information but it was still so very hard.
The one thing I can tell you about children with Aspergers - they are my FAVORITE to work with!! Most are so funny and have great senses of humor. I am current reading a book called, "Freaks, Geeks and Aspergers Disorder," written by a boy when he was just 13 years old. It is such a great book.
Thanks for keeping us updated, Candita. I am thinking about you and your family. I know it will all work out.