You nailed it for me. I have been lurking for nearly a year and pulled the trigger on my first headphones. It was a scramble (with them all on sale) to decide between the HD650, HD600, and the HE-400i, but I don't think I could go wrong with any of those. I'm sure I will be happy. Next up are the Ibasso DX80 (please go on sale) and an yet undetermined amp (looking at Polaris and Schiit options mostly).
To all that have posted listening impressions and amp thoughts in this thread, my wallet hates you, but I thank you!
Holy moly! You bought the 400i's as your FIRST headphone? After lurking for a year?
BTW, sorry about your wallet. Now you have to check out the Mr. Speakers Ether. And Hifiman has a new HE-1000...
I'm kidding in a way. I think the 400i's with a decent amp is end-game for a majority of people. Same for the HD-650, and many many others. This is a true Golden Age of headphones!