@ozzy That is incorrect. The back wall reflection is their one big weakness. The design is so successful because it limits reflection from everywhere else except the back wall. Instead of having to worry about four walls, the floor and the ceiling you only have to worry about the front and rear walls. Line sources also project sound better.
Sound diffusers are best used to kill echos, but again they only work well at higher frequencies. Bass traps are a total and complete waste of money. Four subwoofers is the best solution for bass problems.
Analog crossovers, as you noticed are insufficient. The crossover has to be digital to do everything it needs to do. The problem is now you need four DAC channels instead of two. The MiniDSP crossover is excellent except for those DACs. You can use a MiniDSP SHD Studio and two stereo DACs, but that is going to cost $6 K. The DEQX Pre 4 is way more powerful than the MiniDSP, has fabulous room control functions and great digital bass management. It also Streams and has a MM phono stage designed by Dynavector. I own the Pre 8 which is the same unit with a 4 way crossover. You can triamp your speakers and run subwoofers. I just got a pair of step up transformers. Once I build the complete MC transformer I will comment on the phono stage. It will be a bit as I am still waiting for the Permalloy shielding.