Most home receivers don't have a powered "sub" channel.
If you are using one of the main channels (rear ch?) then yes, you would need a crossover to help it out some.
The box is band pass loaded and cuts out a lot of the high end freqs, but it will muddy the output a bit and cause some strange noises from the thing if you run full range sound into those woofs.
My 2 cents :D
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Robert