those are some others extensions for acoustics (I also saw them on a w810) each of them is use to:

-farfield_call.aec : The sound when someone calls you
-farfield_play.aec: The sound when you play music in the speaker
-PHF_2_call.aec: The sound when someone calls you with the handsfree connected
-farfield_rec.aec: The sound when you record something, I think at the microphone
-Handset_0_call: The sound when you speak with someone (not in the speaker)