I installed a couple of good quality Alpine speakers behind the seats, but the reason I have the booster and plug for the ear buds is so I don’t have to turn the music up so everybody else can hear it.
http://boostaroo.com/uses/earbud
A lot of people that have live sidepipes end up driving with an earplug in so they don’t end up deaf or at the very least with a severe case of tinnitus..
Killing 2 birds with one stone I guess.
There’s probably a better way of doing it these days I’m sure!!