If the subwoofer's amplifier has a crossover built-in, that's all you'll need.

Some people get good results by running their sub full-range, so I know that is possible as well.

Finally, if you're going to be running the rear channels into the subwoofer only, you could use the Empeg's 4-channel equalizer mode and EQ the sub differently than the front speakers.

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Tony Fabris