Theanswer: the t605 needs to be installed, it has a wiring harness etc. It wouldn't be able to talk with two bluetooth devices at once (bluetooth in car and the bluetooth on your phone) The point of this unit is it's a fairly plug and play system that will install bluetooth into your car.
I don't know if it is able to stop music playing through your car cd player when a call comes through, I would assume so, but didn't see anything that said so definitively.
The a2dp is for stereo sound over bluetooth. Some phones and devices have this, if they don't have the specific A2DP bluetooth on the phone/wireless device you would need the aux input to play from an external device as it will not carry stereo music over standard bluetooth.
Dangeris: I think that answers your question too.
Check out this link:
http://direct.motorola.com/ens....html
See how it specifies that only bluetooth music stops when a call comes in? I would assume that because it's actually installed into the head unit it would be able to pause music playing from the cars cd player as well, but why would they specify only bluetooth here? I'd try to get some clarification from your installer.