I've not been able to find a list in any of the Fostex literature of which file-types might be supported by the HP-P1. For those who own it, can you confirm that it supports all formats that are native to iTunes/iPod support (AIFF, WAV, AAC, MP3...etc.)? I was very disappointed to see that the new iBasso DAP does not support AIFF, but understand that it is an Android based system. A good part of my library is in AIFF and the thought of converting some 1000+ albums is not an appealing one.
I'm pretty sure that the signal going to the Fostex is the digital output of the OS audio system in the iPod or iPhone and that is independent of what software is doing the playback.