As indicated just above, I have compared the HiFiMAN HE-6 to the HE1000, also adding in my best-scoring headphones, the Grado GS1000i, to complete the trio for my three-way comparison methods, described in more detail
here.
In this test I used a FiiO X3 playing CD-quality files and feeding out via the SPDIF serial port to my Schiit Bifrost Multibit Uber USB2 DAC. For the two HiFiMAN headphones, I used the HiFiMAN EF-6 amp, especially designed for the hard-to-drive HE-6 and my favorite amp for the HE1000. For the Grado GS1000i, I used the Schiit Lyr 2, low gain setting.
During the tests, I had the most puzzling problem. I was initially using the Apple iPhone 5S, outputting the digital signal via the Lightening Connector into the Apple Camera Kit (converts Lightening to USB), then to a Fanmusic FM-6011, which converts USB (from my Apple Lightening connector) to SPDIF (for my serial input to the Bifrost DAC). However, I found that the results really messed up the soundstage. It didn't collapse it, like a monaural combining of channels would, but it did move the instruments around, particularly putting a guitar normally heard at the right into the middle of the soundstage. If I didn't intimately know the recording from using it in all my tests (over 50 to date), I would have thought it was OK. When I removed the Fanmusic converter from the chain and went straight to the USB input of my Bifrost, all was restored to normal and the instruments were positioned as expected. Strange!! I repeated the tests without the Fanmusic converter.
Suspicious Fanmusic FM-6011 USB-to-SPDIF converter messes up instrument positions
Here are the headphones that I compared:
Comparison showed that the Grado GS1000i (bottom) won most of the acoustic tests, despite its reduced bass, which is so fine on both of the HiFiMAN HE-6 (top) and HE1000 (middle). The HE1000 bested the HE-6 in all aspects except treble detail, as determined by the fine structure of the attack of a finger on a plucked bass, where the HE-6 excelled.
The numerical results are given in the table that follows. As described in the referenced link detailing the test method, a score of 3 (blue) means that the associated headphone was best on that acoustic feature (first prize); 2 (red) is second best, and 3 (yellow) is third best. Ties for second place are 1.5 (orange = red + yellow).
HE1000 outperformed the HE-6 in all tests except treble detail; Grado GH-1000i won out on treble-related tests despite weakest subbass.
The one area mentioned for which the HE1000 headphone falls short of the HE-6 is its transient response, usually noticed as a weaker "snap" to a snare drum impact. That might explain the superior response of the HE-6 to the finger pluck feature of treble detail vs. the HE1000.