Since you were of a mind to use TT's Bluetooth capability (the way the unit communicates with the headset), then you might look around for an alternative, which overcomes the volume problem mentioned earlier.
I settled on the Jabra BT350S. It has a 3.5 mm connector for your MP3 player, and a 3.5 mm socket for your personal choice of headphones. The gadget itself pairs with the TT via Bluetooth. The TT also pairs with your phone, meaning that any incoming phone calls will show on the TT screen, and will be relayed to your headphones via the Jabra. All this time the music plays through the Jabra. When a call comes in it automatically tones down the music.
Now, answering the calls is a little problematic. The Jabra has an inbuilt microphone, but the trick is to get the Jabra unit to fit unobtrusively inside your helmet, near your mouth. Crack that one and you've got the full works.