I am only 5' 8" and have hit my head on the speakers my share of times. I have taller friends who do it too. I have an '07 XLV with the stock tower.
I have never seen it before but what about swinging the speakers to the top of the rack? It won't interfere with the rope or the bimini. Looks aside is there a reason I haven't seen any other photos of people doing this?