As a sight impared individual, I prefer playing my music, movies, and shows at comfortable listening volume levels through open-back headphones in order to be aware of my surroundings. However, I still prefer reference quality. Also, after using closed-backs and open-backs throughout my audio/video journey, I prefer the spaciousness of open-backs. I tried and returned the HD 560S and the HD 400 PRO because I thought voices sounded more like they were being heard through a telephone's earpiece than in person, resulting from a boost I'd say around 1KHz-2KHz. I don't have a meter, but after playing with equalizers every now and then, I think I have an idea of what the various frequencies sound like when boosted and cut too much. Although I didn't try the 400 PRO and 560S within minutes of each other, but I understand they're designed the same way. So if I don't like one, I wouldn't like the other one in the case of the 400 PRO and 560S. I have the HD 559 and hd 599. With the 559, when watching movies and shows, I notice there are times when footsteps and other subtle background noise such as running refridurators, fans, air conditioning, etc. have more bass to them than in person. The 599 has the same bass response as the 559, and also adds some treble boost I'd say within the 5KHz-10KHz part of the spectrum which makes singers such as Andrea Bocelli, Celine Dion, and Enya less mello. The 599 is what I understand to be the Harman U-curve or V-curve. Based on the frequency response charts, the HD 600 seems to be the most neutral. Although perfection would be a design with the bass response of the 560S and the response of the 600 throughout the rest of the spectrum. And with the way technology is evolving, I think THIS should be Sennheiser's NEXT open-back headphones. Regarding Sennheiser's video, I get what you're saying. The 650 and 660S were designed for those listeners who don't like as much treble as originally recorded. That makes sense.