I don't mean to sound like a wowser or a troll, as this sounds like
kind of a cool project, but ahh, I'd say stick with the headphones.
Background sound levels in urban areas continue to increase relatively
unabated, and given the connections between stress levels and noise,
headphones may be more civic-minded. It's bad enough that people want
to start blasting synthesized engine sounds out of (thankfully)
quieter electric and hybrid vehicles.
just a thought
-m