ok this (bttoggle) allows to use a regular headset and listen to music is mono (cant remember I think maybe 8kb) which is low quality and a2dp allows to listen to ur music is stereo which is a lot higher quality and u actually get that sound like ur listenin to ur ipod or cd player with the highs, meds, and lows actually hearing bass and what not. note that this is I'm laymens terms.

maybe this helps.
~mike