The DCX is a far more useful/powerful unit. In addition to being a DSP EQ, the DCX also has extensive crossover capabilities. This will, for example, allow the best possible integration of main speakers to subwoofer(s). In addition, it still allows full precision EQ control over all speakers connected to it, in an individual way(you can apply different EQ/crossover to each separate out put). The DCX also has the very well done GUI to control it via your computer. The DEQ is a straight up EQ, though a powerful one. It simply does EQ functions and has two inputs and two outputs. The DCX can do 3 inputs and 6 outputs.
-Chris