Ed, you did a great job describing both IEM's, pretty much in par with my own hearing experience. Is funny, I never had the sibilance described by W3 owners, although certain music, especially sopranos like Kathleen Battle would at times pierce my ears with the W3 but not with the UM3X. It is much easier to sleep with the UM3X than the W3's, for me a very important fact.
I am thinking of custom sleeves, But I am not yet sure because a softer material than vinyl may be preferable, Also important would be to make sure they remain flush so you can sleep on your side without pressure from your pillow.
For some reason, the black olive foams take some of the bass and sound brighter than triple flanges and large Comply's. Would UM56 retain the bass and highs as or better than the universals?
Again, thank you for your nice review.