I have exactly the same problem - I have just updated from snow leopard to Lion and, as the 'multiple speakers' option worked fine before, I can only imagine this has something to due with a fault in Lion when running itunes 10.6... be great if anyone has a fix for this. I use this a lot to stream music and radio from my macbook Pro to various parts of my home (interestingly my wife has the same machine running lion and itunes 10.5 and she has no problems with airplay for multiple speakers. grrrrrrr.