if you're not using a Tube amp (OTL especially), you're probably wasting your time and money.

Modern music doesn't exactly equal "hi-fi" and therefore you must get something that suits modern music. I don't think a neutral headphone does well with modern music since many people are looking for bass and "smooth sound." So, something like the HD800 or the 650 is not the most dynamic (ironic because they're dynamic driver headphones) nor does it have the most fun bass. You should look elsewhere if you don't like the HD650 nor have equipment to feed it. Get a HD700 (jk).

I understand your sentiments exactly. I also own HD650 (and HD600) ant think that HE-400i is superior to both of them. The sound is more detailed and also more musical. I have used HD650 with quite high-end amplifiers and believe me there is a limit to how much they can scale. By the way HE-400i sounds as "natural" as HD650. The sound is more extended in both ends and timbre of the instruments is truer through HE-400i. The details are there, the sound is more open and airy. There is space around the instruments and the background is completely black. I listen mostly to acoustic music, jazz and classical and Jeff, I can assure you that HE-400i is a real hi-fi headphone. 

I love you music station!!