I upgraded my roadglide audio , and also purchased a cheap mp3 player I plug it into the aux input on the stock radio. Went for a ride and noticed that the radio had to be turned all the way up to really hear the mp3 player properly, but I needed more volume. When i got home I remembered that I had this mini head phone amp that is powered by a 9v battery. I attached it to the inside of my fairing pluged it all in and now I can turn the mp3 player up so I can really hear it. I mean it works great.
just thought I would share this.
Thanks Here is the site. http://www.headbangeramps.com/

 

Nice find. Pretty interesting.