I have a question related to this: So you have your .wav files, or mp3's or what have you, stored on your computers hard drive in digital form. You send those out via the ethernet to your 811g compatible wireless router, which in turn passes on the digital information through the airwaves to the airport express airtunes receiver which is connected to either an amp, or some amplified speakers. Am I correct so far? So where is the digital to analog conversion taking place? Or, is a DAC required at one end or the other?
As far as having multiple speakers is concerned, it seems to me, given my understanding is correct, that you could send your signal to your airport express airtunes receiver via the wireless (btw, make sure to get an 811g and NOT an 811b as the later may be too slow for a streaming audio signal), which is plugged into an amplifier (integrated or separates), and add a speaker selector box to the output of your amplifier, such as Niles or Bryston makes, to send that signal to several sets of speakers. Of course this requires hard wiring the multiple sets of speakers to the switch box, and with all speakers running will be at some compromise to the power of the signal to each set of speakers, but certainly would be an adequate method for party music.