S.H.
Google gender disappointment and maybe you will get an idea of what he is feeling. And I think sometimes it is harder for men to have it, for they don't have any connection with the baby until it gets here. And that connection we have with a baby while in utero is amazing...we are so attached right away. Its not like that with men.
Let him grieve the loss of the dream of him having a daughter. It doesn't have anything to do with the new baby. They are two seperate issues. He will get over it. It may not be quick, and may take until he sets his eyes on his new son, but he will.