Larry, if I follow your suggestion, you propose a TMMMMT configuration, with two of the Ms being the 6 1/2" driver and the other two the 5 1/4". This would seem to provide for more bass extension(but all four Ms being 6 1/2", and using the same enclosure height, would allow even more), with no difference in the horizontal dispersion factor that brings some objections.
As Jason points out, we have speculated about a possible W M/T W, configuration that some centers use(if a generally horizontal configuration is insisted upon). This could use the 6/1/2" driver for the woofers, crossed over at maybe 300Hz, with the standard 1" tweeter immediately above the 4" mid used in the QS4 and crossed over around 3000Hz. Such designs exhibit a smoother and wider horizontal dispersion because of the vertical alignment of the tweeter/mid assembly. The enclosure would have to be higher, maybe 9".
