Android/Linux USB audio driver compliant with FiiO USB DAC E7:
"The FiiO E7 Headphone Amplifier is an USB DAC dedicated to high fidelity headphone.
It works out of the box with my Ubuntu 11.04. I just plug it when I need it and several seconds later it appears in my output sound devices list."
FiiO E7 Headphone Amplifier (Audio Devices) - Linux Hardware Compatibility List
"Buried in this thread is another person who successfully used his Beresford Caiman USB DAC on an Android tablet using USB Host. It's pretty easy to get working, all you need is an Android device with CyanogenMod7 support and USB HOST enabled. You need a powered hub for it to work though."
USB headphone AMP with Android Phones, possible ???
USB Audio Driver for ALSA "usbaudio.o" is likely missing in the current stock kernel of Android 4.0.3.
"Usbaudio.o" is present in the mod kernel of the Nook tablet which allows FiiO USB DAC E7 & Nook to interoperate:
[webcam support] USB Host support that YOU can try (now in nightlies) - xda-developers
xda-developers - View Single Post - [webcam support] USB Host support that YOU can try (now in nightlies)
"Usbaudio.o" is likely not present in the 4.0 kernel and FiiO USB DAC E7 doesn’t interwork with Google Galaxy Nexus:
Samsung galaxy nexus
For the time being, Google is not aware of the USB DAC market, and the USB DAC manufacturers do not know the Android devices, likely the predominant computer systems in the (near) future.
Likely, Google architects are aware that computer systems should be compliant with standard computer interfaces like USB:
USB Host and Accessory | Android Developers
And, likely it's not the case with some Google program managers:
. USB Host feature not activated in Android 4.0.0
. no support of USB Audio in Android 4.0.3.