with a 2 seat sports car, that is a convertible, you need to give up on quality and go for quantity if you want to hear it with the wind noise. You need spl's to enjoy music with a top down. Dynaudio speakers and McIntosh amps are available, but won't sound any better than Alpine or top of the line Sony.
I would suggest looking for an MTX Thunderforms sub to fit in your trunk, if they make one for your B'mer. JL Audio makes the same type enclosure for about 3 times the cost, but in a convertible the additional speed that you are getting for the price will not be noticed.
I would then get some Alpine digital amps (the 4.150) to drive both your sub and your speakers. For speakers, I would look at the higher end, and power handling Polk, Alpine or Boston Acoustic. JL's are great, but won't handle the volumes you need with wind noise.
For a head unit that you want, I would suggest a high end Sony, Eclipse or Alpine, and I would blow off the disk drive and just make sure it has a good iPod interface. If your iPod is loaded with AppleLossless or Wav files, the DAC in the headunit will sound fine.
PS - if no trunk subs will work, there are some really cool below the seat sub modules that really work for convertibles.