Most people have all their music on their phone these days. I too own an iPhone and an iPad. These devices have both Bluetooth and AirPlay for wireless transmission of the music and video to speakers and monitors.
I purchased an iHome wireless Bluetooth speaker on Amazon.com for about $59.00 and mounted it with velcro to the inside of the top bin board on the hatch. I simply turn the hatch board around when I am out sailing to listen to music while underway. I am free to move around the boat and control the music from my iPhone.
If I watch any videos on my iPhone or iPad the sound from the movie comes over the Bluetooth speaker also.
The speaker has pretty decent quality and volume but will not vibrate the boat like a 1500 watt stereo some kids have in their cars. It is a sailboat so this small speaker works just fine for me.