can one get audio output simultaneously from the USB and analog line out?

You can hijack the audio from any application, or the system audio, with Audio Hijack Pro

<http://www.rogueamoeba.com/audiohijackpro/>

You can then use its Auxiliary Device Output effect to send the audio to multiple devices.

I was recently pleased to discover Mountain Lion has this in the Midi Setup utility as "Create Multi-Output Device".

http://support.apple.com/kb/PH5178

In Audio MIDI Setup, click the Add button (+) in the Audio Devices window, and then choose Create Multi-Output Device.

A new multi-output device appears in the list on the left side of the window. To rename the device, double-click it.