Configure outbound thread pools in JBoss EAP 6.4.4

I'm implementing a SOAP application (A) running in a JBoss EAP 6.4.4. This application is calling several other services using outbound SOAP and REST calls.

I made some performance tests with a request that calls via (A) another service (B), running also in a JBoss EAP. Both (A) and (B) have the same inbound HTTP connection/thread pools configured.

With high load (A) has a throughput of 6.5 messages per second which is not a lot. Calling the (B) directly I have several hundreds of requests. So my conclusion is that there must be a problem with outbound thread/connection pools in (A). The system has long to open a connection from (A) to (B).

(A) is doing more interaction with the database, but the difference between 6.5 and several 100 is huge. So it cannot only be the database IO.

How do I configure them in JBoss? For outbound SOAP calls I use CXF and for REST I use RESTEasy.

Thanks for any input.