Just download MP3s at 256k or better and you'll be fine. I demoed my car the other day for a guy who explained his home system to me. He has what must be a $250k system. This stuff was so expensive and esoteric that I'd never heard of any of it--a $50k turntable? Anyway, he loved the car, claimed it had the highest resolution he'd ever heard in a car and that the dynamics were as good or better than what he has at home. Then he insisted that he could hear the difference between ANY compressed format and CD on any system. After 15 minutes of him railing against digital equalization and fake-sounding processing, we listened.

I think I upset him when I told him that the tracks he had chosen were all iTunes downloads at 128k and that for those tracks, there was nothing going on above 15k, and that all the amplification in the car besides what drives the subwoofers are 20-watt ICs. When I broke out the PC and showed him how much EQ and processing he was listening to, he said, "This causes me to rethink my hobby."

Mission accomplished.

Oh, back to the original topic: I've never heard anything that claimed to restore the sound of low bit-rate MP3s that worked as well as boosting the high frequencies that are left by a dB or two. If it's the lack of high frequencies that has you down, try that. If you download at 256k, then even that isn't necessary.