you could do like the 2013 cvo road king and put a set of speakers in the lower fairings and saddlebags. use a small bluetooth amp, or ram mount mounted to your handlebars. run the cable to the input on the amp
I did the Sena headset and Bluetooth music to it...incredible sound. Also makes for easy communication when riding two up. Highly recommend it. For summertime, use a half helmet and have a Kurakyn sound bar. Works very well up to about 75. Sound quality is good but not great but works well for my purposes.
go to ebay and take a look. on my 07 road king i had the handle bar mount. it was a 1000 watt system made by Polk Audio. it wasnt the same as my ultra classic but it worked fine for 89.00
I have seen a post from Scootluver on here that I’m going to attempt on my king. I searched sound systems road king. Was the best looking in my opinion