I don’t know what you mean with QandA Traffic?
The DAAP client will send out a question asking whether there are any servers on the local subnet. If a server receives this question, it will reply with an answer containing the specifics of the service(s) being offered. So, knowing this information will allow one to discern whether a) the client is sending the query (something which is evidently taking place, since running DAAP from within iTunes works) and b) if and how the server is responding (a deficiency which both Ron and I seem to agree is at the root of your problem).
Before proceeding, which version of mDNSResponder are you using? The current release is 107.1.
If compiled in toto from source, a utility named mDNSNetMonitor is created. Running this will output the zero-conf traffic on your subnet. Having not run the open-source version of mDNSResponder in a couple of years, I cannot comment on whether the following applies to that release, but… Beginning in early 2004 (v.58 ff, I think), Apple integrated the ability to poll the daemon (mDNS) directly for its status. Issuing a command such as:
sudo killall -info mDNSResponderPosixmay dump information concerning any active beacon(s) and the service(s) being broadcast to the system.log. (This tech document contains an overview.)
Herman