Believe it or not it sounds like their requirements pretty much match the Standards of Care. Basically anyone who's a PhD or above can write you letters. The first letter should come from your regular therapist (Hopefully you've been seeing them 18 months!). The second letter is simply a letter verifying the case information from the first.
The trick is hoping Aetna doesn't try to screw you by saying they don't recognize the persons credentials or some such. So give them the information on the providers and see if they are okay. Your endo doesn't count because he isn't a mental health professional. I would ask your primary therapist for a name of someone to see for your second letter. Then, after checking with Aetna, see that person. A second letter usually only requires one of two appointments.
Also, before you go any further, you might want to check to make sure Aetna doesn't have any more surprises for you. Ask them can you see the surgeon of your choice or do you need to see one of theirs. Another problem you might run into is finding a surgeon that'll accept insurance. You could end being asked to pay up front and hope the company reimburses you.
I haven't used insurance myself, I paid everything out of pocket, but you might find some people who did here:
Lots of college aged kids there.