Hi Arun,
The merge response is required as separate intermediate message if you have request and response independent interfaces running in async mode,
request : bpm to soap (async)
response: file to bpm (async)
in that case you need to wait for response and correlate to the running BPM.
as you mentioned in your first question that all interfaces are async, but then we discussed different scenarios and as you are doing this for your proof of concept you can start with this, and let me know if that works.