How many speakers can you drive with Airtunes?

I know apples knowledge base doc ( http://docs.info.apple.com/article.html?artnum=108038 ) says that you can have a maximum of 3 to 6 sets of speakers maximum. However, in practice what have people managed to achieve?

I managed to get 2 speakers going but had problems with 3 with the airport expresses as clients. Moving to WDS and the AX's as remotes now means I can get music to stream to 3 speakers. See this post http://discussions.apple.com/thread.jspa?threadID=1399864&tstart=0 for more info.

Has anyone got more than three to work successfully?