So I recently purchased a FiiO L3 for my iPhone to use with an external headphone amplifier.
 
I'm wondering what exactly the L3 does to the iPhone's audio processing. I know LOD connections bypass the internal headphone amplifier, but do what audio don't get bypassed?
 

1. I can't seem to make/take phone calls with headphones plugged-in to the external amplifier, so I would need to unplug the headphones to answer an incoming call
2. While playing a game, the audio doesn't play through the external amplifier either; I tried plugging-in the headphones into the iPhone's standard headphone jack and the audio plays just fine (volume is controlled with the iPhone's volume rocker too)

Iirc all 30 pin more or less have a command on what the iphone is supposed to do when its plugged jn,  most lod tells the ios device to pass music/ medias into it,  the reason why games audio doesnt pass through is that the game is not programmed to output the audio to the lineout,  as for why you cant answer the phone is also the same,  since the lod doesnt have the command to hook it to the phone.  Fiio made a mic+ amp once though that you can do to both answer call and amp