So i have an airport express, and a personal laptop, and am finally ripping my CDs. Years after everyone else...
I don't use crossmixing playback, but you can tell iTunes not to crossmix continuous albums which is all very well
But even with that flag it doesn't apply a similar soundcheck value to all the tracks, so you still get a noticable volume shift
blech: iVolume reuses the tag for volume normalisation, but is more configuable. Not sure if it handles albums.
There's also MacMP3Gain.