Since JA has written expensively about using iTunes and Apple Express for music streaming, I thought it might be useful to point out an apparent change in iTunes 10 that affects streaming.
iTunes 9.x when used for streaming, previously had an option under Preferences/Devices to "Disable Volume control when using remote speakers", which, when checked, allowed a full range signal to be sent to the AE. This was true whether using the AE's digital or analog out (I use digital).
The option has now changed to "Allow iTunes control from remote speakers", but it does not seem to work the way the previous option worked. In fact, I am not sure HOW it works, as toggling it on and off did not seem to change the system behavior. The "Help", as of this morning, still referred to the old option.
The new behavior causes the iTunes volume control to effect the output from the AE at all times.
I use the Remote App to stream from iTunes to an AE, and find that the volume control accessible via the iPod Touch's Remote App now raises and lowers the volume from AE, even when using the digital out. The good news is that when the volume control is at maximum, it appears that the AE outputs a full range signal, the same as when the previous option for "Disable..." was checked.
But I can not prove this as I have no means to assess whether the output is still bit accurate to the source as it was in the past, per JA's reports on the subject. I did do an A/B between a stream, and the same CD played from a CD Deck, both feeding my DAC, and the levels appear to be the same.
That said, I would much prefer to have the old option back.