I don't think the tzar350 sounds anything similar to the er4-s. Way, way too much treble on the 350. Conversely, the 4.ai was way too warm.
To me the Ety's are not bright iems in treble. However they are very clear and have edge due to the upper mid peak, between 2k and 4k, they tune to compensate for being in ear, versus over the ear.
So it sounds like the noble 6 most likely doesn't have the upper mid presence of the ety. I'd like to hear a comparison of the noble 4 from a die hard ety fan, as I'd love to find an ER-4s replacement In a comfortable form factor.
My first serious IEM love was the Etymotic HF2. As good as it is the N4 is simply better; it's more detailed with greater extension and an effortless sound. The upper mids are a little less warm than the HF2's so you'll give that up for greater clarity and technical ability. You'll also get a far larger sound stage. For me the HF2 was intimate and never created even the semblance of dimensionality, the N4 does.