[uab9253]

Are you mixing to wave file? Try doing that and listening to it while still on your recording PC - there should be NO difference with sound. If there is, check your export setttings to make sure your automation, eq and effects are being included in the export. I suspect that the iTunes and cd player differences are a combination of loss due to conversion to mp3 compression and/or the different systems you are listening on.

Getting a perfect mix in the studio and then hearing it squashed by a poor car audio system or MySpace stream is something we have all had to learn to deal with in different ways. Many people cut test mixes and take them out to play on multiple systems, take notes, and then bring it back for remix. What a pain, but unless you have a really flat reference that you can trust, this seems to be a necessary evil.