It sounds like you have your default gateway set to the endian box, then endian is routing packets to your router.
Your PC -> FW -> Router -> Server B
Remember endian is a firewall, it looks at all the packets, and most likely its getting picked up by a linux firewall rule and droped as abuse.
A better setup would be to setup your router(10.0.0.
as your pc's default gateway, and the default route of the router, the firewall.
Clients -> Router -> FW