Cannot get APM to replace my Citrix Web Interface servers (5.4)

Hm...at this point you should probably be doing tcpdump to see what is happening with the communication between the BIG-IP and your XML brokers. You can also enable VDI debugging on the BIG-IP using this command:

tmsh modify sys db log.accesscontrol.level value debug

After you run it, a lot more Citrix-related stuff will be logged to /var/log/apm - so that might give you a clue. Don't forget to set that value back to "notice" after you are done debugging.

You can also open a case with F5 support to troubleshoot the issue.