Ben Weiss: I'm afraid N -> N is not something for which we have any plans. While there are a small number of folks such as yourself who could make use of this, the vast majority of our users need 1 -> 1 or 1 -> N, and that's what we'll continue to make. Sorry!

While not supported in anyway, and having the possibility to cause glitches with your Preferences, you can copy Airfoil, and run a second instance to send your second source to other outputs. Again, not supported, but it will likely work.

Rick: By default, I believe the sleep is 30 minutes, yes. And when it's asleep, the ATV disappears as a source, in iTunes or Airfoil.

However, you can adjust the sleep pref in the Settings, and there's a "Never" option, which will mean it will always be available.