This is a well thought out and written review. Unfortunately far too many of today’s audio reviews are based more on advertising revenue than actual substance. I own the HD600, HD6XX and Nighthawk Carbon and IME your descriptions of them are spot on.
I use EQ with all of my headphones because it gives me the ability to tailor them to my particular listening preferences. I am amazed at how well the HD600 and HD6XX scale with better electronics. The Nighthawk Carbon is as you say, a polarizing headphone.
It had some poor reviews early on which led to a mass sell off and huge discounts. Audioquest significantly lowered the Nighthawk and Nightowl Carbon’s price more than once.
Due to poor sales they were quickly discontinued, which is unfortunate, since with a few changes they can actually sound quite good. I had read that the headphone cable was
largely responsible for the sucked out midrange on the Nighthawk and Nightowl Carbons.
I purchased a different cable and have found this to be the case with my NHC. The cable change and some light EQ makes the midrange sound significantly more open. Yet, the NHC remains a darker sounding headphone with (at least to my ears a pleasant tone).
Theses headphones are also incredibly comfortable for longer listening sessions.
It’s getting tougher to find them on the used market. And even more difficult to find them in nice condition. I’ve seen factory sealed ones selling for upwards of $500 and in some cases nearly $600. I paid $175 for a new pair minus the case and extra ear pads.
It was still a great deal.