Any way to buy replacement motherboard for DX4000? (Ethernet port issue)

I was in your position and the only way to get back to where you were is another DX4000 box. You can pick these up on ebay. I then installed a USB ethernet:below:
StarTech.com USB 3.0 to Gigabit Ethernet NIC Network Adapter - 10/100/1000 Network Adapter - USB to Ethernet LAN Adapter - USB to RJ45
I am using my original server with no problems.