In theory it should be possible to play music from the Nexus 7 on a Kenwood KDC-BT755HD radio via a USB cable when using the Kenwood Music Control App. So far, using the the Kenwood Music Control app, has not worked. On the Nexsus 7, "auto output" and "output right now" can't be selected. I suspect that the Kenwood Music Control application may be limited to smart-phones. Has anyone connected the Nexus 7 to a Kenwood radio using the Kenwood Music Control?

Music lists stored in your Android™ smartphone can be managed on the navigator screen. Songs can be easily selected by searching for an artist or album name.
Connecting the Android™ terminal in which this application is installed to the Kenwood car audio system with a USB cable allows you to control playback of songs; for example, selecting songs according to an artist or album name.
Create your favorite playlists so that you can enjoy music whenever and wherever you want.

* To enable playback control from the Kenwood car audio system, you need to select "Preference" → "Analyzed data output settings" → "Output right now" or "Auto output" to create a song database on the SD card. After connecting your Android™ terminal to the Kenwood car audio system, you need to set its USB storage mode to On.

* If your Android terminal is not ready for MSC (mass storage), it cannot be controlled from the Kenwood car audio system. For how to turn on the USB mass storage, refer to the Manual that comes with it.
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Connecting the Nexus 7 to the Kenwood via bluetooth works as expected. Also the Pandora app worked too. So the fact that the Kenwood Music Control is being troublesome, is not too serious. But I would still like to resolve the issue.