I join the two others who say the Elear's bass is nowhere near in extension and slam to that of the TH900. Also, it is a different kind of bass, the TH900 oomph is lower, so it's a bit like apples and oranges. Both have strong points and weak points.
What struck me more: my modded TH900 sounded much more open and with way better mids than the Elear, which was more closed/shut in/veiled/wooly. Taking a look on the ear pads, I think it's possible to improve on the Elear -- for one I wonder how the Utopia pads would sound on the Elear.
Overall, the TH900 is more colored than the Elear, but the Elear is colored, too, and I think it is safe to say the stock TH900 is the better of the two, for me. Perhaps it should be, as it's more expensive than the Elear.
My second listen to the Utopia went better, but even if it was a closed headphone with similar price as the TH900, I would still think twice which one to get, but given the price difference, the choice is easier
. The Utopia really needs good amps (bass-heavy but transparent tube amp would match best). I like both my Stax 007's (Mk1 and Mk2) and the 009 over the Utopia. I also like the HE1000 more.
Anyway, I have yet to find a headphone with better deep bass than the TH900. The Audeze XC didn't make it for me. I've never heard any Ethers. Perhaps the new HE1000 v2? (But even then, I need a closed can).