well, i can start you looking in the right direction for using your ipad as a source.
you'll need a transport, to acquire the digital signal from your device.
sure, the ipad can be connected to a usb dac via the "camera connection kit", but a dedicated transport will work more reliably, and will charge your ipad while playing.
look at these:
Pure i-20 digital dock
Cambridge iD100 digital dock
as far as headphones... you'll get much further by sifting through the various threads and clicking on the "head gear" section of the forum.