Ah, so the "M100", which I've made facetious reference to in the past, is about to become reality.
Ian, the Thiele-Small parameters on the new woofers would be of interest, especially the max excursion and Fs.
Alex, a high quality 6 1/2" aluminum cone woofer might run about $60 as a guesstimate(we don't know the parameters), although some are over $100. Then of course there would also be software modifications needed.