Many self-powered subwoofers connect via the main speakers connections or via the amplifiers output terminals so having a sub output on the amp is irrelevant.This is fine, but I would NEVER use a signal coming off a subwoofer that would ultimately drive my main speakers. And that was the point of my post before.
With a speaker that truncates the bottom 1.5 octaves, no cabling, equalization or speaker positioning is going to help with this. It's either a subwoofer or another pair of speakers altogether.