I got a pair of HD6XX headphones and sent them through Sonarworks for the individual calibration service. It took a very long time round-trip and communicating with their customer service was frustrating. I believe they allowed me an educational discount.
I quite like and recommend the individual calibration service with the headphone edition of the plugin. I appreciate the low-latency and phase linear settings available on the plugin. The graphs of the frequency and phase response, adjustments, etc are pretty and at least let one know what exactly is going on, unlike some competing products from Waves and others. The measurement PDF that one gets with this service is sort of neat to know and have on record too, especially when one has multiple pairs of headphones for people to use.
The Sennheiser headphones with model numbers 600 or greater are all flat enough with decent bass extension to achieve good flatness when using the plugin without weirdness. I bet that planar magnetic headphones with their excellent and quite flat bass extension could be calibrated and get great results as well. In terms of amps, all the Schiit products, especially the ones not involving tubes, are certainly adequate or even great for use with this. I have my heart set on picking up a Little Labs Monotor soon, but admit that the Schiit Jotunheim, Mjolnir 2, and Ragnarok (all the balanced ones) are tempting. I found the RND RNHP to be fine but edged out by the Monotor.
I'm dubious about using Sonarworks stuff with and for loudspeakers, and know the variances between pairs of some headphones to be great enough that using the plugin with the averages they provide as opposed to a curve based on measurements of one's actual pairs seems dubious to me as well, but I find it useful with the individually calibrated headphones.
I also don't like the systemwide applet's annoying/tenacious behavior on macOS very much, despite the convenience and quality of the sound, and also dislike that the profiles for my specific pair of headphones live among the averages for silly headphones I'd never be caught wearing that repopulate automatically after being manually deleted.
- This reply was modified 5 years ago by Samuel Botstein.