I also use Foobar2000(with LAME) for all my flac/shn/wav/etc>mp3 conversions, but I also use Foobar to sync with my Ipod...there is an older plugin called foo_dop that works like a champ. Itunes is/was way over-bloated and caused me nothing but problems, I had to reinstall my OS to completely get rid of it

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Regarding 24bit>mp3 I don't think there is an issue at all..at least currently, I believe the LMA does this, and I have done it many times with Foobar/LAME, I have yet to notice anything out of the ordinary compared to 16bit>mp3.