Thanks to a friend, just finish to install an Airport Express 2nd gen. (a1392) connected to my android device. (you can do with a dedicated smarthone, tablet, etc...)
My friend said his airport have some optical output problems with firmware above 7.6 (sometimes works sometimes not). Mine is 7.8 and works great, probably is the Android system, we don't really know.
Pretty easy and works great. With wifi audio streaming the quality is totally lossless, also the airport sounds amazing, great dynamic and soundstage. Totally noise-free of course.
What you need:
- Airport Express 2nd Gen.
- 12 volts relay
- 12v to 3.3v step down converter (very cheap on ebay)
- DoubleTwist Pro version Android App for the streming ($8.99)
What you have to do:
- Open your airport and remove al screws.
- Remove internal power supply, it's a separate box and comes out very easily with help of a flat screwdriver
- Use the relais feed and activate ad feed the step-down (the airport need not less than 2-3 Ampere to works fine). Use remote out (from head unit, dsp...) to activate relais.
- Use the 3.3V step-down output to powering the Airport.
I put on everything on a wood board just for test, wired, and used an electrical terminal to connect easily to power, ground and remote from DSP. You can use a better-looking box, etc...
As said, it works with Apple devices too of course, but not sure about the firmware.
Hope this help someone. Feel free to ask more info!