sadly usable specs are hard to find. typical IEM manufacturers spam us with buzz words and keep actual data for themselves. so aside from trying to measure stuff yourself or be lucky enough to find someone who did it with your particular combo, you're mostly in the dark when it comes to objective data.
as
@bigshot said, what headphone/IEM you plug in a device is a significant variable, and not just as a matter of having big power numbers(which ironically is almost never the real problem). plenty of devices just plain suck when driving a low impedance IEM, and then many will work fine, but because of some impedance interactions, the IEM's signature could change audibly. but again that depends massively on the IEM used.
you could find some clues from fellow members like
https://www.head-fi.org/f/threads/t...urements-in-post-3-tutorial-in-post-2.800208/ it's amateur measurements done by several people on different rigs, so I can't warn enough about not taking everything at face value. but for example, while the measures are limited to the frequency response of devices, as many are done with specific IEMs plugged in, we can often guess if the impedance of the device is high or not just by looking at the FR graph.
it's not much but it can be enough to avoid some products to drive our IEM if that's a variable that counts for it.
the common sense advice is to avoid using headphones/IEMs that have atypical specs because that multiplies the chances for a device not to be designed to drive it. but it means that first we have enough specs about the IEM to be able to tell, we usually don't. and at the same time, we're often attracted by gears because of how different they are(or claim to be) compared to typical gears. so ... ^_^.
