I recently purchased the nice box for the Ensemble RXTX from the KM5H store and it does make it into a very professional looking little software defined radio.
The audio labels are ambiguous, "line in" means "this connection goes to your line in". There is an amazing bit of python/C software called Quisk that can be used to control the Ensemble.
Here it is receiving a station from Kuwait (I'm in Sydney by the way).
To get this working on Ubuntu 12.04, I did try using the install from the Ubuntu software centre but I couldn't get it to talk to USB so I ended up simply downloading the software, doing a 'make', and running it from the command line.
Quisk comes with a config file preset for the Ensemble RXTX at quisk-3.6.2/softrock/conf_rx_tx_ensemble.py which I copied to ~/.quisk_conf.py and edited to point the audio to my creative USB external sound device.