Ah... My current receiver has an RCA rear sub output though it lacks a small or large setting for the surrounds. My ignorance. I totally buy into the single subwoofer being very non-directional angle as my computer speakers have the subwoofer about four feet to the right of the main speakers and when listening to, say, Barry White, I could SWEAR that the lowest registers of his voice are coming from those 2" drivers.
Having said that, if it was at all possible, I'd like to have a -3dB point of no lower than 80 Hz if possible, even on rears.