I've never known mine to be able to do this, and the fact that in the manual (p.59) it says that while Airplay is going, selecting any other input will stop Airplay playback makes me think that it's not possible.
Workarounds would be to (a) buy an HDMI splitter and run one cable through the receiver and the other directly to the TV to bypass the receiver when Airplay is on (might cause handshake issues) or (b) use an external source to play iTunes music into the receiver. Neither of these is really a convenient solution.
If it's important to you, maybe ask a new, more general question whether any receivers have this capability. I'm not that any does.