no problems for the long post my friend!
thanks for being so thorough when explaining! it helps other posters/reader to better understand what your saying by providing a better context to your inquiry!
anyways
i find the biggest problem with your assessment of the amperiors vs the hd25 is what i bolded above.
and here is my reasoning for that
take a look here: These are the specs for the hd25-1- ii (assuming you have this one ofc)
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THD, total harmonic distortion | < 0,3 % | |
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Contact pressure | ~ 2,5 N | |
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Ear coupling | supraaural | |
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Jack plug | 3,5/6,3 mm stereo | |
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Cable length | 1,5 m | |
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Transducer principle | dynamic, closed | |
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Weight | Without cable: ~ 140 g | |
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Nominal impedance | 70 Ω | |
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Load rating | 200 mW | |
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Max. Sound pressure level (active) | 120 dB | |
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and take a lookie here on the amperiors ( i couldn't find them on the sennheiser website but i have my personal amperiors here with me with the box
THD, total harmonic distortion | < 0,3 % | |
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Contact pressure | b/a | |
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Ear coupling | supraaural | |
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Jack plug | | |
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Cable length | | |
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Transducer principle | dynamic, closed | |
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Weight | | |
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Nominal impedance | 18 Ω | |
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Load rating | ???? | |
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Max. Sound pressure level (active) | 120 dB | |
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its obviously not complete but here is a link to it (not sure how credible this is) but click on the impedance compared for me anyway it shows the sennheiser hd 25 (alu) which supposedly have the same drivers as the HD25 but with the aluminum earcups (not sure if they are acoustically identical to the amperiors
but you can see in that graph the impedance is much lower
and if you assume they have the same spl which is what we see here..... it should tell you that the amperiors are more efficient > the hd25 = it requires less Voltage and power, essentially to drive the amperiors > the hd 25
so if you compared them at the same volume, then the amperiors would naturally be "louder"
also i haven't heard the cx 300 II (but i have heard their successors the cx 3.00) which i found quite warm and dark sounding (somewhat treble-deficient) so they would sound much much smoother and easier then the amperiors if they were given the same volume and voltage essentially
so essentially you can't exactly compare the hd25 and the amperiors directly based on "volume" even if the same song and device and such.
but lastly like you said even after all of that, the amperiors aren't comfortable to you and you still find the hd25 more to your liking, whether its due to your listening volume, genre preference or your current equipment.
just go for the hd25, or if anything take them from your brother and buy him a new one!