iTunes sounding rather spiffy since Quicktime update 7.6 yesterday
I did the Quicktime 7.6 updates yesterday evening but have not listened to iTunes until the last 30 minutes or so.
I was sampling tracks from Black Uhuru's "Dub Factor" (iTunes+ 256K AAC) and playing some lossless Bowie tracks and noticed the bass has got more grunt than usual.
Turned the wick up and was quite pleasantly suprised. Sounds just like the jump in quality when I installed the dedicated PSU for the DAC at Christmas-time (and that cost £105 to achieve!)
Quicktime is the audio 'engine' for iTunes on Windows. Not sure if Mac users will benefit directly as iTunes on a Mac uses 'Audio Midi' (I think).
Let us know if you hear anything similar (or not).