What is the difference between the 435 and the 335 technically and tonally?
This a misconception. UERM uses only 3 drivers, and it's reference level, and sounds fantastic. Number of drivers does not equate to better SQ. ER4 uses one BA, and according to lots of people it's very accurate.
Although roxanne uses 12 drivers, it's still 3-way crossovers.
Which is why, Lukalop, you have to go and listen to some IEMs. Rather than do a desktop theoretical analysis. Numbers don't always add up. Implementation is key.