BIG-IP LTM and ASM - Read xml package to extract information and redirect traffic

in a normal forwarding or proxying scenario, in order to get the XML response, the bigip already made a load balancing decision. You can inspect the traffic and pick up the reference id, the easiest would be to parse the HTTP::payload. Examples here: link text

Once you made the decision on where to forward the traffic next, you can chose the node via the "node" commmand and rerun the request through the proxy using the HTTP::retry command. link text

An alternative is to use a sideband connection to probe the server and analyze the response before the BigIP makes an LB decision: examples can be found by searching on this site.

HTH.