what you can do
as test is
in the Firewall Portf.
add forwarding with incomming all to Server_IP1 with port 80
and
add forwarding with incomming all_IP but Port 81 to Server_IP2 with port 80
but outside of the efw you can connect aaaa.com goes server 1 port 80
and bbbb.com:81 goes server 2 on port 80
i this this will work
beacause on my quick overwiev i have not seen anything but tomorrow i looking again