To update:
Progress maybe just to the side tho!!
Two servers: 192.168.1.200 & 192.168.1.201
Urls: 1.a.com, 2.a.com, 3.a.com, 4.a.com.
The two servers are set up as peers within the Webservers Tab of Reverse Proxy, they are both listed on port 80 and have their relevant IP address listed.
subdomains 1 and 2 are meant to go to 192.168.1.200. 3 and 4 should go to 192.168.1.201.
Everything is going to 200.
Ideas?