I spent entirely too much time on it today, but I finally got it so we can stream music to two different Airport Expresses. I've been wanting to liberate the living room speakers from their wired oppression for some time and Misa bought another airport the other day. Like most Apple products the setup was quick and easy, but the signal to the bedroom speakers kept dropping out when trying to stream to the living room ones simultaneously. I fixed the problem by doing a manual configuration and setting it up as a WDS network to support internet in the bedroom (damn cement buildings). Then, based on some online recommendations, I changed the multicast rates (the default is 2Mbps) to 11 - there's a Spinal Tap reference in there somewhere - on all of the Airports and it seems to have fixed the problem. For good measure I also made sure that interference robustness is being used.
