I have some bad news for you…what you’re trying to do might not be possible…or the best idea for what’s left of your hearing.
I’m not a doctor. But even with extreme deafness, I don’t know how safe it is to be listening to headphones in excess of 126 decibels. That’s loud enough to damage the physical structures of your ears almost immediately in a sealed headphone environment. So I wouldn’t recommend doing this at all regardless of the current health of your ears.
I’ll try to explain a little about why you’ve had such difficulty in spite of what’s theoretically possible.
The number you want to look at in headphones specs for volume capability is sensitivity. This tells you how loud the headphones are rated for with a standard basic amp, usually. Most headphones have a sensitivity rating around 100dB. Some are a little lower, some are a little higher…and you’re right, higher resistance headphones tend to have lower sensitivities.
The other number that’s sometimes useful is power handling, which shows the maximum theoretical amount of power the headphone can take before you break it. I’ve heard some stories about certain models, such as the M50X, being able to take legendary amounts of power before dying…but I’ve never done any tests like that myself. I rarely listen to a headphone at anything louder than 90dB, and when I do it’s only for a few seconds for my review process at most.
Also, distortion is going to start to be a huge problem in more ways than one at the volumes you’re talking about, even if the headphones don’t die. Most headphones have their THD (distortion) ratings done either at 90 or 100 decibels, because they figure that’s the maximum sound level most people will use them at. Beyond that, the engineers worry less about the driver cone breaking up or wobbling because it’s so loud that most folks will take the headphones off before ever hearing the distortion.
So even if you do find a pair that will go as loud as you need it to, I can almost guarantee that the sound coming out of it will be an awful honky distorted mess that has the potential to physically damage your head and ears.
And that’s before we even consider the digital side of this problem. A standard DAC at 16-bit/48khz is only going to have 96dB of dynamic range to its audio. That means the difference between the loudest sound and the quietest sound it can push out to the amp is 96dB. So if you take that and amp it up louder, that has the potential to add distortion inside the source before it even reaches the headphones.
Hi-res DACs with uncompressed non-DSD hi-res files can get up further, to around 144dB of theoretical dynamic range…but again, once you’re playing audio that loud, it’s going to be an awful distorted mess anyway.
I’m sorry I don’t have better news for you. You’re pushing against the limits of physics and also risking further damage not just to your ears but the areas surrounding them in your head. I know it might be tempting because you’ll think “well it’s already gone anyway, what have I got to lose?” But volumes that loud are still dangerous to you and anyone who might be nearby, if you can even manage to achieve them.
Please don’t do this!!!