So, my old PC died, which had all of my iTunes music (mostly ALAC). I built a new PC, turned on my electronics, and started playing stuff via AirTunes (optical out, of course). Boy did that suck! Very, very weak bass, and the highs were harsh to the point of being painful. I started panicking. An electrical surge during a storm fried my old PC. I was going to cry if my nice, new DAC, pre, and amp were fried, too. So, I switched to a CD player hooked up to the DAC. Wow, everything sounded great. Now I thought that maybe I had imagined everything sounding great through the Airport Express.
Long story, short: On the Windows version of iTunes, the EQ was on by default, and set to flat. Yikes! Once I turned the EQ off, and disabled AirTunes volume control, it was as great of a setup as I remembered.
Argh!!