anyone listened to iTunes Plus on high end system?

Just curious if anyone has taken a recording of an iTunes plus AAC 256k file and compared an actual CD version on a high end system. I know AAC is "lossy", but was wondering if there was a human ear difference. On my low to mid-fi system, I cannot hear a difference. And I have really sensitive ears. I'd like to hear from the high end world.
no question that there is an obvious difference between Apple Lossless and AAC

you don't need a real high end system to hear it
I tested a version of Jennifer Warnes' rendition of "Ballad of a Runaway Horse" from the Famous Blue Raincoat recording, comparing a CD burned from an iTunes plus download against the original AIFF CD version of the same release of the same song, and there was not doubt the AIFF had more detail and musical information. This result was noticed on a modest Panasonic Blueray player with digital out to the DAC in a Decca integrated amp and played through Vienna Acoustics Beethoven Baby Grands. Both versions sounded good, the AIFF file on the factory made CD sounded better, with more subtle details of the recording discernible.

How much difference you hear will certainly depend on the DAC you are using - HQ outboard DAC will reveal more of a difference than the DAC on you Computer or iPod. But all components in your system will contribute as resolution increases throughout. I would think that on very high end systems, the difference would be quite striking. The same way a good SACD recording often trumps standard red book versions.
Thanks Knownothing, that was the type of answer I was looking for. I believe my weak link is my speakers. I tried a comparison with a classical piece (cd version compared to itunes plus), there was more dynamics and air on the redbook compared to the cd I burned with the aac file. The first test was "hard rock" which was quite a bit compressed in the first place. It was harder for me to tell a difference. The 256 acc, however, did sound quite good and if I did not have the original CD, would have been quite happy. I hope HD tracks keeps expanding...and hopefully, Apple will have lossless downloads one day.
Note - just in case someone is tracking along - there is a big difference between what Abery is listening to - AAC@256 and what Knownothing is referencing which is AIFF (uncompressed format)

Absolutely no comparison
For what it is worth - it usually doesn't take a remarkably good system to tell the difference between standard iTunes 128kps AAC fiels and iTunes Plus 256kps AAC files. The Plus files usually connect the musical dots better in every way.