I actually had a speaker a while back called the Elsinore's I believe. Also DIY. They used MTM up top like the X-MTM's but then used another 2 woofers for bass and midbass re-enforcement only. The extra woofers rolled in right where the baffle step happens and allowed for a simplified crossover. It was a 2.5 way design. Very clever design and also really good bass (still needed a sub though, IMO). I think I ended up running mine fully active because I was trying to deal with acoustic bass issues in my room and I eventually went to full OB because I found that no EQ was every sufficient to deal with the bass issues I was facing. OB solved all of that nicely, in one fell swoop.
But aren't you getting the Mockingbird's soon? If so, I promise you, once you get them in your system, you will not be listening to any other speakers, the new line arrays will completely outclass any other speaker.