I found a nice looking Modern radio with retro look on ebay, here is the URL for it. It even has the knobs like the old style radios, but plays the modern gear, CD, MP3.USB, SD card ect.. CD is hidden, cool looking. 4 channel, 40 watts per channel. I was thinking maybe you could combine both front and rear channels to make 80 watts, but I don't know about that. It is a nice thought, but I don't think it will work that way. Anyway, 40 should be enough. Maybe put two more speakers in the back.
The only issue is that you have to cut the cycle sound to fit the single din face. I don't like cutting these things up.