Sean, it's the other way around; 6dB is the least steep. Generally, steeper is better(except that some audiophiles make a fetish of preferring 6dB first-order crossovers), and the THX specs for receiver crossovers call for a 12dB/octave high-pass to the speakers and a 24dB/octave fourth-order low-pass to the sub.

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Enjoy the music, not the equipment.