Make sure you have "Soundcheck" turned off (in iTunes' prefs) when A/B-ing an ALAC file w/ an AIFF flle. The volume of an AIFF file doesn't appear to be affected by Soundcheck, thus, it'll play back at a higher volume than the same file in an Apple Lossless format. This can cause ALAC files to sound "kind of dead and flat" compared to AIFFs, but all things being equal (i.e., audio levels) they sound quite the same to me.