I recently bought a BT transmitter from AMZ so I could transmit from my good ol' iPod to the Echo. Actually, I bought two different ones because each had some unique features. One is only a transmitter and the other is a transmitter/receiver, so I could make any standard stereo headphone BT-capable using the BT receiver.
These are the two I purchased:
MPOW:
http://www.amazon.com/gp/product/B00P20TFWM?keywords=mpow%20streambot&qid=1447184615&ref_=sr_1_3&sr=8-3 I like this one above since it is a transmitter and receiver, but it can't do what the other can:
Tao Tronics:
http://www.amazon.com/dp/B00GKEAQ2M/ref=sr_ph?ie=UTF8&qid=1447184880&sr=1&keywords=taotronics This one is a transmitter only, BUT it can charge while being used; the other cannot.
-- Both were easy to set up.
-- I can charge both with an old 5V cell phone charger w/mini USB connector.
-- Both sound great either through Echo or headphones.
-- They are tiny and light weight: the size of a matchbook!
-- Both cost less than $30; the transmitter-only is the least costly, but not by much.
I usually use the Tao Tronics since I mostly just transmit to Echo from iPod and it can charge while in use. Get this one if you only want to transmit.
So far, the gadgets have worked with what I connected them to: the Echo, BT speakers and headphones, and even helped my old-tech transform into modern tech by enabling the iPod and wired headphones to be BT devices!
If you have a BT-capable computer, it can also connect it to the Echo. I play music playlists from my NAS on network to Echo. BT is very handy.