Sure, I saw that example. Maybe let me put it a different way: if a client has one inbound FIX connection to HAProxy, can HAProxy connect to N backend servers and send each FIX message from the single client connection to a different backend?

It seems like it could:

  use_backend fix_servers_a if { var(txn.sendercompid) -m str firmA }
    default_backend fix_servers_b

Then "fix_servers_a" could be defined as a round-robin backend.

I have not tested that use case but I do not think so. It has the ability to parse FIX tag values and make routing decisions from the initial Logon message.