There are ways to overcome the Allison effect, as it is a near-corner-positional problem, a function of the distances, similar or hopefully dissimilar, meaning staggered, from the woofer to the three near boundaries. It does not require a horn or even a separate lower-mid driver. You can locate the woofer right near a boundary (or two, or three) but have it cover well up above middle C, like to 300-400Hz. Or you can suggest / enforce that its distances from floor, front wall, and sidewall are staggered 2/3/4 or 2/3/5'. Or, finally, since it is to first order independent of listener position (it is NOT related to room resonances), you can EQ it out with a canny bump to compensate for the inevitable lower-mid dip.
Although the new BasX line of products are relatively inexpensive, it doesn't mean you can't assemble quite an impressive home theater system that can rival more expensive solutions. The MC-700 coupled with a BasX A-700 gets you a full separates solution for about the same price as a midpriced AV receiver. Sure this combo may not have all of the bells and whistles of an AV receiver, but you do get the very important PEQ function (especially on the subwoofer channel) and flexibility to upgrade in the future as technology evolves. Amplifiers rarely go obsolete, but what do you do with the processing section of an AV receiver once it does?