I'm interested in the graphics amplifiers as well. That's dook Dell/Alienware released the hardware to work explicitly with their systems. There are alternatives but I would prefer something manufactured by Asus for my Asus G75VW, the GTX 660m isn't holding up as well as it used to. The rest of the components are still excellent though. A graphics amplifier would beat buying a new system...
ViDock is popular, but I can hold out for Nvidia or Asus to produce an alternative.