I rip all of my CD's to FLAC (lossless) format onto my Linux machine that is used by Squeezecenter for my Squeezeboxes. I wrote a program that creates MP3 files from the FLAC files in a parallel file tree, and this is run every night to seek out the new FLAC files that don't have MP3 equivalents. I point iTunes at these MP3 files. It took some effort, but it works like a charm now.
Michael
Michael