Clark,
Actually, when posed this question I always tell people that if you have the budget then I would suggest a new head unit, amplifiers, and new speakers. If your working on a budget then I would go this route in this order: New Speakers, Amplifier then change the head unit. The new amp and speakers will do most of the work, the head unit comes down to functionality.
Let me know if you have any other questions,
Martin-RPM
Actually, when posed this question I always tell people that if you have the budget then I would suggest a new head unit, amplifiers, and new speakers. If your working on a budget then I would go this route in this order: New Speakers, Amplifier then change the head unit. The new amp and speakers will do most of the work, the head unit comes down to functionality.
Let me know if you have any other questions,
Martin-RPM