I found an App called Remote HD, which allowed me to connect to the ATv (1st gen, but should work on 2nd Gen too).
This app requires you to load a "Remote Helper" component on the ATv in order to control it. The nice thing about it is that the helper works as modified AirPlay speaker on the ATv (shows up as "Apple TV-RHD"). Now DS Audio sees the ATv as a speaker, and it actually works pretty well.
I'm not even sure you need the app for this. I think if you just install the Remote Helper, it should work too. Here is the link for the app: http://remotehd.com/AppleTV/Download
So far so good, I can now play all my iTunes library on my living room, without using the desktop, just an iPhone or iPad!
Not sure it matters, but just in case, I'm using IOS 5 on the iPhone ans iPad.