Yes, two more "flavors" of custom IEMs!
Let me start by saying that if it was really all about the number of drivers the UERM wouldn't have compared as well as it did. Speaking based only on technical ability, tuning and design does play the primary role in how things stack up with the exception of the bass region. While a single bass driver can reproduce a good amount of bass for most music, there are some challenges with authoritative sub-bass when compared with a dynamic driver. And since I mentioned the bass and sub-bass, most BA implementations have tighter bass but don't reverberate the same way as the dynamic driver bass.
There seems to be a loose correlation between the number of drivers and/or crossovers and the level of detail/resolution with more drivers and crossover points resulting in more detail. However, with the exception of the SE 5-way, the differences aren't huge between the SA-43, UERM, JH16, and LS8. And as a note, I break it into two categories, instrument detail and overall resolution/detail. Instrument detail is essentially instrument detail meaning how much detail each instrument has, such as how defined is someone's fingers on a harp or how much reverberation of a string can you hear and experience. Overall resolution/detail is how the whole presentation is put together including instrument separation, how well defined the lines between each music creating component in the music is and the black space, and the actual black space which, when combined with the soundstage components such as proportion and overall size result in a recreation of the music. Two good examples IMO are the EM3 Pro and JH16. The EM3 Pro has great resolution of the ambiance in a recording but below average detail resolution while the JH16 is the opposite, primarily because of the soundstage proportions, however also in part due to the slightly analytical presentation.
Ultimately it comes down to this: making custom IEMs (or any audio equipment) is an art with a basis in physics (engineering). Why were Leonardo da Vinci and Van Gogh better than others? Hence, it is not necessarily based on the components in the custom IEM, but the engineering and artistry making listening and comparing is necessary.