Well that's just the thing - nobody knows how much of an improvement (if any) we will see in practice. Because you're right when you say that the Miracle/Merlin/plenty of other high end customs already sound fantastic.
The idea is the same as it is with active crossovers in speaker systems. Basically you've got the spectrum being separated into the appropriate range for each driver, maximizing clarity and minimizing any crossover induced distortion.
How will it play out in real life? Will it sound clearly better than a Miracle? Will the UM box, with it's all in one approach, be able to outperform a dedicated high end transport/DAC/amp setup? Only time will tell.
Great post project86! There are loudspeaker manufacturers that use active vs. passive crossovers and they aren't considered the best speakers. I have heard some stunningly realistic speakers that use passive crossovers, but due to size constraints, CIEM crossovers have limitations so I am very interested in hearing what an active crossover can do.
My thought about how I would test it is use the coax out from the DX100 (or the Musiland Monitor O1 us -> external DAC) and then I can A/B easily both the Pure 6 active vs. passive and the Pure 6 vs. other CIEMs.