For the past year or so, I have been using a bluetooth receiver to stream music from my ipad or android cell phone via A2DP. It works great. I simply turn on this small device and plug it into the aux jack on my stereo and I can play tunes without being tethered. I really enjoy reading the bios in Pandora as the music plays. The downside is that the BT device is rechargeable and has a limited range. I had to string a long cable up into the cockpit in order to play music from there which is kind of pointless with a wireless device.
About a month ago the stereo died. So I went out and bought a Sony unit with built in BT. This also allows us to use the stereo as a speaker phone with our cells. But this unit also has a distance limitation and in the cockpit, the music would often cut out.
I did a little online research and found that the antenna in these head units are very small as they do not need to connect from very far because they were designed to be in your car which is pretty small.
I found that if I added an external antenna it should increase the range so I popped open the stereo and found the mini coax connecter on the BT module and connected it to a standard 5db gain 2.4ghz antenna(similar to a wifi antenna). I could now go to the boat in the next slip and stream my music all for about $25. I also gain by not needing a separate powered device.