Hi Tarek,
I suppose you have knowledge with former AS versions.
Throw the knowlege about ejb-clients away, it's complete different.
Since AS7 the Proxy (stub) does not contain any information about the server, it is only a implementation of the Interface that is created by reflection during runtime lookup().
The Proxy knows only the name "ejb:app/module/distinct/bean!view".
If you execute a method the ejb-client library decide how to go, here is the knowlege what server exists set by the initial creation or the jboss-ejb-client.properties.
The selector handle the phys. connections to the servers and I'm not sure what happen in your case setting the selectors for each call, regardless that such sync-block might be a concurrency bottleneck.
Le me finish my example I mentioned above and it might will give you an idea.