Do yourself a favor and sit in a F30 335 with an aftermarket exhaust. These youtube videos give you an idea of the tonal qualities, but hearing it in person will blow you away with the volume. Not to mention a better connection to your car. I liken it to listening to your favorite band live in a small night club with the amps set to 11.
The speakers OTOH - let's be honest, the car is not an optimal setting to listen to music, and once you improve this, then you have to improve that, then you have to dynamat the door panel, rear deck etc. Plus you bought the car, so no worries about losing equity on the purchase, having to swap out blah blah
You can put a fantastic stereo on an Accord, while you can never make that car sound like your N55 uncorked. I can also say that with the exhaust your windows will generally be down and your stereo will be off
You probably know what I'd go with...