I don’t know why Lotoo hasn’t released the OI details, it’s not as if they’re shy about providing other specs! I searched pretty thoroughly for it a couple of months ago - I was leery about buying it if the OI was too low - so it’s possible that information has been released since then. I also asked on head-fi and no one could provide an answer. I ended up taking a risk on a used S1 from Musicteck assuming that I could sell it on without too much of a hit it if it didn’t work out. But it’s fine for my tastes.
That’s interesting @Titienne about the difference between the 3.5/4.4 outputs and is well worth noting, thank you.
I’ve compared my S1 against the iPhone with dongle, the Fulla 2, and the Magni 3, and all have an OI below an ohm and closer to zero, IIRC, and all sounded much darker than the S1. (This is without using any of the preset EQ settings on the S1).