If yours is under the seat then it will be more complicated. The wiring for the power and speakers is also behind the dash, so that isn't a prob, but you will either need to extend or reroute the wiring for the display, aerial and steering wheel controls.
Also, the Cabasse stereo has a different display, so if you were hoping to get a display adaptor this may complicate matters.
What are you hoping to achieve with the new head unit? If it is just iPod control and Bluetooth, you might instead consider the Parrot Mki9200.