I've not tried on my motorized bicycle yet, but I wore headphones as a matter of course with all my motorcycles. I've had at least a half dozen different helmets (fullface) where I inserted full size headphone speakers into the hollow spaces in the liner where yer ears go, then wired a jack in the back so I could unplug and take the helmet off w/o getting all tangled.
"Without music, life would be a mistake" - Nietzsche
Honestly, kept at an acceptable level as to not damage your hearing there's little danger with listening to music whilst riding. What with the scream of a two stroke and the wind roar, there's little to hear anyway. Should there be something you need
to hear, like a truck locking brakes, a car's horn, or even the dreaded siren - trust me you'll hear it just fine.
If you get worried, like yer downtown or something you can always turn it down or off. We're not talking about trying to dial a cell phone or something here lol It's just another matter of using your (un)common sense
I'm still tweakin' my ride, so that's the only reason I've not done it w/my motorized bicycle yet. But you can bet on the fact I'll be jammin' out on any distance rides in the future \m/