Can tracks managed with iTunes be input to this unit's USB sound card (audio interface)?

Yes. When DJM-S9 and the computer are connected and a track is played in iTunes, the sound is input to the DJM-S9's channel 1. It cannot be input to other channels. Also, files containing DRM data cannot be played.

If sound is not input when the above operation is performed, do the following.

Windows 8.1 and 8
Select [Run] from the [Apps view], enter [mmsys.cpl], and then click [OK]. The [Sound] window opens. Select "PIONEER DJM-S9" on the [Playback] tab of the [Sound] window.
*This cannot be used simultaneously with the ASIO driver.

Windows 7
Display the [Run] dialog box from the [Start Menu], enter [mmsys.cpl], and then click [OK]. The [Sound] window opens. Select "PIONEER DJM-S9" on the [Playback] tab of the [Sound] window.
*This cannot be used simultaneously with the ASIO driver.

Mac OS X
In "Select a device for sound output" on the [Output] tab in [Sound] of [System Preferences], select "PIONEER DJM-S9" from the sound devices. DJM-S9’s input channel can be changed by selecting "PIONEER DJM-S9" in [Audio MIDI Setup] of [Applications] > [Utilities] and then using the [Configure Speakers] dialog box.