You need to set your voice options to both. It's currently set to headset most likely. Its under preferences. That will record other peoples voice. Not yours
click the guide button go all the way to the right under settings... look for preferences... select voice.... select both.... Done
Your not going to. You would need a cable that would go from your controller and split the audio cable going from the game to the pvr to do that.
You would prob have to get it at an electronics store like radio shack. It would take your headset jack on your controller. split it in 2 . then a cable that would go from that and convert it to 3.5 mm then convert that to the composite source. Not worth the hassle. If you want to do commentaries use it for that. Just use something like Sony Vegas to record your commentary after. I would recommend looking in the premium downloads section and download the new version of ArcSoft. It came with my PVR 2 and the software has a commentary feature built in. So you can commentate over the video once its recorded.
Avermedia Live Gamer HD or Blackmagic Intensity Pro would be the best options for capturing your voice while commentating.
You could get a mixer.. your game audio and headset can plugin into that and you choose the loudness of the in game audio and your voice
The nice thing I love about the Avermedia Live Gamer HD. You can record your commentary and it saves it as a separate file. You don't have to use it if you don't want to