Received my GO 720 today. At first I had a heck of a time trying to figure out the volume. Glad this thread clarified it for me. Seems to me that the GO internal volume should be set to a maximum (without distortion) and the OS should control the volume. Now, I agree with most that has been said. It is just a bit on the bright side, not objectionable but titled in that direction. Using HD800's and listening to Time Out DSD64 via Audirvana+, did I hear a couple of clicks? Not sure but listening very closely and if there are any they are very intermittent (of course, there should be none). I'm somewhat troubled by the max volume necessary to listen at my normal "detailed" volume level. A+ is set at -10db. This seems to indicate that the max volume output is just a few db's up. Is this correct or do I have the volume messed up still? Overall nice tone and detail, a "keeper". However I'm having difficulty getting the USB to fit tight enough to stay put either with the extension or directly into my MAC Pro Retina.
I can only get to 50% before getting my HD800s up to "way too loud" on my Go 450 on Windows 8.1. Not familiar enough with Macs to help with your settings, but either you listen much louder than I or your settings are off.
Also, the more I listen, the more I like it with the T20RPs and the HD650s, but just a bit too lean with the HD800s. Great resolution, detail, etc., just not enough heft to be a perfect match. Only a touch disappointed since the HD800 was one of the reference headphones - I had hoped for a slightly more synergistic pairing. I hope that the Pulse X will be a touch weightier with the larger power supplies.