Did a 511/414/500 Hz dbx digital XO MTM for a large basement HT long before 'HT' became popular and they rocked. With an 811 the accepted MTM 1 WL XO point spacing limit dictates a max ~1300 Hz.

Having built numerous TMM layouts, I don't much like them unless either a very low XO point that allows < 1WL acoustic XO spacings is used or I'm far enough away to make them appear as a single point source, otherwise I prefer a 9844 tandem woofer layout. The TMM can work extremely well though if the bottom woofer is rolled off to create a TMW 2.5 way.

GM