Okay, here you go (FXT90 vs. DDM). I used the E7/E8 (Fiio DAC/Amp) combination out of my Mac to do the comparison. To get to the crust of it right away, there is not fair comparison. The FXT90 smokes the DDM (and the DDM has been one of my favorites for a long time).
The DDM sound veiled and muddy compared to the FXT90 (this even with my DDM having hundreds of hours on them now and not even a good five hours of burn-in on the FXT90). The JVC has great instrument separation; more micro-detail of instruments; more clarity and transparency than the DDM. The JVC has better treble.
Now, mids are a hallmark of the DDM. Mids and bass. So the mids are more forward and in your face (somewhat) than on the FXT90 (this doesn't mean the mids on the JVC are the least bit recessed, they are not). But despite being forward, the sound is way muddier coming out the DDM.
Bass is where the DDM is king however. Yes, the DDM has quite a bit more sub-bass in quantity than the FXT90 (and JVC has quite a bit). But the FXT90 blows the DDM away in quality of bass. I really only used one test song for the both IEMs, Lenny Kravitz' "Are Gonna Go My Way." There was so much detail and liveliness in the JVC as compared to the DDM. They both do thick notes, but again, way more clarity in the FXT90. The bass of the DDM is not bad (don't get me wrong), but it's not clear compared to the FXT90. Timbre is nice in the DDM (and it has its own special layered sound like no other), but it still doesn't compete well against the JVC.
The treble of the DDM can't even get into the ballpark of the FXT90.
Only clarity I've heard in a dynamic approaching the FXT90 is in the GR07 and Sony 7550 (although neither throws out the intensity of energy in the guitars the way the JVC does - GR07 is much much closer).
Sound quality I would put the DDM at a 5 compared to a solid 9 (1 to 10 scale) for the FXT90. Hope that helps. Happy listening.