I do not know what effect these conversions you are accomplishing within iTunes will have on the SQ of the files. I have not tried it myself. More important is using Error Correction on the original rip, as well as the ripping software that implements that correction. As far as the double conversions, in theory, all those file types are bit-for-bit. You may want to try one, then rip the same file directly to AIFF and compare the two to see if there is a loss in SQ. Just a thought.