I don't understand how you say that you need a specific output impedance for certain ohm rated headphones, can u teach me lol?, i mean if you look at it from a totally newbie perspective, every amp i mentioned says a range of like 16-300/600 ohms for headphones, regardless of what the impedance is 10 or 16 ohm, so why is it recommended to use a lower impedance? sorry to ask so many questions lol. also about the my question i asked in the first post, don't suppose you have an answer to that? the e12 looks nice, as you said that the k550 isn't really a bassy headphone, if i tried a amp first with athm50's say the e12.
For getting the best audio quality from a headphone, it's recommended that the headphone's impedance (Ohms) be at least 8 to ten times (or more is fine) the impedance of whatever it is plugged into.
It's not a requirement, more like a guide line.
I plug my 50-Ohm headphones into an amp with a 10-Ohm impedance, so that 5 times the impedance and it sounds fine.
I can also plug my 600-Ohm headphones into my 1-Ohm O2 amp. So that 600 times the impedance, sounds fine.
Chances are your motherboard front speaker/headphone output has a high impedance, could be 30-Ohms, 50-Ohms, 75-Ohms, etc.
If you plugged an external headphone amplifier (like the O2, Magni, E12, etc.) into the motherboard's line-out/headphone jack, the motherboard's impedance is no longer a factor, just the external amplifier's.
For trying to figure out if a headphone will provide the right amount of power (mw) to a headphone?
It's really just up to you and the volume knob (or volume setting). You just up the volume setting (voltage) until you get the loudness you want.
The higher the headphones impedance, the more voltage is required to overcome the impedance and drive the diaphragm, that is inside the headphone's cup.
Outputing a lot of voltage is very very easy, but with the diaphragm in the headphone cup (and speakers), it how that voltage is applied (with a headphone amplifier) that counts.
The ATH-M50s usually sound about the same no matter what they are plugged into or amplifier used.
But the E12 should be a fair bit better (quality wise) at driving headphones, then the motherboard.
So I would expect the (38-Ohm) ATH-M50s to improve, using the E12.