Yes, you can unlink ringtone and notification volume on Android 6. To do this, follow these steps:
1. Open the 'Settings' app on your Android device.
2. Scroll down and tap on 'Sound'.
3. Tap on 'Volume'.
4. You will see separate sliders for 'Ringtone' and 'Notifications'. Adjust them according to your preference.
Now, your ringtone and notification volumes will be independent of each other.