Wouldn't a pair of Sennheiser HD-600's and a whopping subwoofer be an excellent install?

I suspect it may be illegal to wear headphones but I wouldn't expect to be stopped for it due to window tinting and general police malaise with traffic stops.

i'm sure it would be fine for you. what about when other people are in your car? i personally would like to have headphone restricting my movement in the car not to mention the wires. with the money you spend on headphones i'm sure u could get a a component set. just my 2 cents

I don't know about that. Stictly on a sound basis, I don't think Headphones can reproduce the depth and imaging like a properly tuned system can. Just my experience from what I've heard.

a good set of headphones can do all that .

Headphones are generally good at imaging but not staging.

Wearing headphones in a car is indeed illegal and quite irresponsible IMO.

A set of HD-600's which are open backed headphones would allow you to hear the outside world better than running a set of comps at any decent sound level. I don't see the irresponsibility at all - now those people on cell phones I could talk about all day.