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"Have about 700 CD's on iTunes in the format iTunes records them."
The first thing to do is figure out what format was used to rip the CDs into iTunes.
Click on your Music library in the left column of the iTunes window and look at the column labeled "Kind." You may have to scroll to the right to see that column. If you don't see a Kind column you can turn it on by going to the View menu in iTunes, choosing "Show View Options" and clicking on the Kind and Bit Rate boxes under the "File" section in the window that opens.
If the songs were ripped as mp3 (MPEG audio file) or the similar AAC format you might want to consider re-ripping at least your favorites. If they were ripped as AIFF, WAV or Apple Lossless any improvement you get by re-ripping is probably not worth the effort, all will sound essentially like the CD.
You choose which format iTunes uses for ripping by going to Preferences under the iTunes menu, clicking on Import Settings under the General section of the preferences and making a choice from the drop-down menu.