I haven't used foobar personally. I did sighted comparisons between my iPod playing compreesed tracks vs a CD player playing the originals. My pre-amp is a Meridian 201 and allows for inputs to be volume matched. I would cue up the devices so they were playing the same track in sync time-wise, as much as possible, then used the remote to switch between sources. For moderate to high compression rates i couldn't hear a difference. Thinking my hearing was possibly not that great, I got others to listen also, they couldn't hear a difference either.
Equipment used: iPod classic 3rd gen, Micromega stage 2 CD player, Meridian 201 pre-amp, Perreaux 6000B amp, B&W 802 Nautilus speakers.
I have also used Sony MDR-D77 headphones.
In response to HiFi critics, I created a file containing interleaved segments of 223 kbps AAC and uncompressed source, which I uploaded. This doesn't require Foobar or anything else special for playback. I ask people to tell me the time codes where the edits are. No one has so far. Here is the file if you are interested: https://rapidshare.com/files/3023221...3AAC_short.rar
Foobar is a better approach, but requires a PC or windows.