Add a property and get the session bean to use a selector.
Or use different queues for the replies.
I can never understand why people do this kind
of processing what is wrong with invoking a session
bean on server2? You obviously don't need it to
run in the same transaction (it wouldn't work if you did)
so you don't need a DTM.
SB1 (server1) -> SBx (server2)
If you need to make it available through JMS as well,
you just do:
MDB (server2) -> SBx (server2)