i not really a pro in AAC conversion but, i can say that AAC really weakened your music. i not sure (once read b4), VBR where it only take the important bitrate of the music and discard other less important to create a compress music.

up to now, using mp3 with 320k compression still the best for me.

ya, like me, if i use apple loseless compression, which equivalent to FLAC the sound is good on my in ear phone. after all is classical music, which i cant afford to lose any nice instruments lol..