map pool member ip address to domain name

If that's all you want to do, you could use an HTTPClass profile with each pool member in a different pool.

Or you can do in iRules using a switch statement, or using a datagroup lookup. Here is switch example in HTTP_REQUEST;-

switch [getfield [HTTP:host] : 1] {    
    "mycompany.com.au" -
    "yourcompany.com.au" {
        pool [LB::server pool] member 1.1.1.1
     }         
     "theircompany.com" {
        pool [LB::server pool] member 2.1.1.1
     }
     default {
        pool [LB::server pool] member 3.1.1.1
     }
}

Let us know if you want any more information.