I recently downloaded and tried this software with my Hifiman HE-400is. I found it changed the sound dramatically. At first, I didn't quite like it, but after getting used to it, I find I cannot go back to the stock sound of these headphones.
It dramatically increased the sub-bass, which I found strange, because I thought theses headphones were relatively flat down in the sub-bass region. At least, when I look at Innerfidelity's raw measurements, that's what it looks like. However, Sonarworks measured a step roll-off just below 100hz. To try and confirm which measurement is more accurate, I decided to play a number of test tones in 10hz increments, starting at 100hz, and going all the way down to 20hz. Sure enough, without Sonarworks software turned on, the test tones quickly become fainter and fainter the lower I go, confirming that Sonarworks measurements appear to be accurate. With Sonarworks turned on, these headphones can now play what sounds to be relatively flat down to about 40hz. And like I said, this makes a huge difference.
I'd like to have a bit more flexibility in shaping the frequency response, though. For example, Sonarworks measured a dip in the response around 2khz and so EQ'd upwards to flatten this out. Maybe it's just me, but I think I prefer a slight dip in this region, otherwise it can give a somewhat "shouty" quality to certain recordings. However, Janis from Sonarworks told me they are working on introducing additional EQ customization for the user, so this will be interesting to see.
