Are you using an external DAC?
If you are using an external DAC,
are you controlling volume with
the iTunes user interface, or with the DAC?
If an external DAC, what interface are
you using between the computer and the DAC?
You might find it best to defeat the iTunes
equalizer altogether: un-click checkbox on equalizer
widget top left.
Importing directly to iTunes, error correction 'on',
Apple Lossless, will give you bit-for-bit at playback.
*All other things being equal*, your music server should
sound exactly like a transport. Mine does.