Gotcha - there are limited headphone choices for audio enthusiasts in truly lightweight on-ear form. Glad you like the ones you have. I see by the blue FiiO logo that it's using the SBC codec, though Avantree says their unit supports AAC (cyan logo in the BTR3) and aptX (purple). Have you seen it connect to AAC or aptX? That could make a noticeable difference.  Ahh, the Avantree Cara II is a receiver, so that's obviously not in play in your picture. What is transmitting there?