Is your Bengal girl able to "talk" to him behind closed doors? For her to be able to adjust to his presence, she must be able to communicate with him while he is in quarantine. She should have the run of the house (or whatever part of the house) she had before his arrival. Basically, you don't want anything in HER routine changed. HE should adapt to HER routine. So, if and when you attempt introductions, again, they should be done to minimze any disrutpion to your girl's normal daily routine. Remember, cats are creatues of habit and do not like change. So, the idea is to try to minimize any change for her. After all, it is HER home and SHE has to accept HIM, not the other way around.
If your girl does not accept him, and being that she does not like the Manx very well either, she may just be one of those cats that does not do well in a feline "community" and she may have to have her own portion of the house where there are no other cats. It may be that the Savannah and the Manx will get along better than the Bengal and the Savannah, if the Bengal is a "loner" type personality.