I wasn’t expecting it to be this this fast but my ER-4P is back today. Etymotic tested and confirmed the problem and then replaced both (not just the broken left channel) speaker unit. So essentially I got a new ER-4P with the old wire. I gotta say after some extensive listening to K701 and DT880 for a few days my hears have heightened its sensitivity and know what to “listen for” from a pair of phones. Half-excited, I plugged in my ER-4P into my Bithead amp using the low impedance setting and started listening, and, surprise!
In my opinion, ER-4P beats the crap out of K701, DT 880, and the HD 595, at least on my Bithead amp. ER-4P wins by a landslide in areas of sound resolution, tone accuracy, volume, and isolation. Compared to the ER-4P, K701 sounds smudgy. DT 880 is close but not as accurate as it should be. HD 595 just doesn’t have the same level of balance as other phones.
I assume the problem is due to my amp: my Bithead is sufficient in driving ER-4P and HD 595 but not K701 or the even more power-hungry DT 880. Unlike the ER-4P, K701 and DT 880 just can’t do their best on my source right now.
So for now, ER-4P > ALL.