I am not sure if I have completely understood. However to balance the load for the Web UI between different application servers you want to use load balancing mechanisms. Did you check the Sizing Guide of Product 360 already? There is a chapter called "High Availability with Load Balancing". Maybe this can lead the way for you?!
Any suggestions on how to configure the Load balancer for the WEB UI? Cant get it to work using IIS. I get to the login page but cant login for some reason.
Is there an easier way using Apache instead of IIS?
maybe this two KBs can help because here you will see which extensions are also called via Proxy
One of it contains also infos to IIS
If you ask my personally I would always favor Apache over IICS. Also our internal dev test systems use Apache instead and IICS did not behave in perfect manner in other customer deployments of the past as well. But that's just my two cents. In theory IICS should be possible...