What sort of test, exactly? Unless you got the actual dB's, chances are you're listening at a higher volume when for example you have better headphones and amps. Why? You get less distortion. A less capable system will have you pulling back earlier because distortion is already audible.
Also there's a chance that if you are indeed listening at a much lower volume now than with the 900X before, then that previous headphone/system could have damaged your hearing before you got the new one. Whatever it is, consult some ENTs. Not just one, because as much as doctors might be medically trained, once in a while you can encounter someone who would tell anyone (who might not have tinnitus) to not listen with headphones at all (kind of like when a woman encounters a doctor who I can't go any further because the mods might flag it as a political discussion even if it's just an example, but I suppose you can guess where I was going there).