The CP650 model designation by itself is the digital processor WITH EX & Digital Cinema capability.
The CP650XO adds the built in crossover for seperating the woofer and tweeter in the front channels. There are other models, the 650D (without EX or DC capabbility), 650SR (without digital sound altogether).
I would reccomend the CP650, even if you will not be spliting your surrounds, because if you install DC later you'll have to buy EX card anyway.
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