By the way, later than promised, but I got nice tubes placed in my WA3+ and am finally getting enough breathing room from relentless deadlines to try what I said I would: run the UERM (as well as my UE11 customs) through the tube amp (fed by a CIAudio VDA2 DAC and VAC1 PSU, optical input provided by a Mac mini running Audirvana).
And yes, Cee Tee was right - against my expectations, frankly, it is worth a try to play these low-impedance in-ear monitors with a tube amp that is designed for higher impedance headphones (I usually pair it with my 600 ohm DT880s). The sound is remarkably crisp and airy, compared to using the same IEM on my Hifiman HM-601 with the same sound file.
That said, it's not going to be my go-to combo: I like the IEMs when I travel, I still like my comfy Beyers for sitting down at my desk at work or at home. I feel like with my portable amps, I have tweaked in a certain synergy the IEMs benefit from, and my tube amps do well with the Beyers. Mixing these set-ups is kind of messing with my clear alternatives...