I use my own personally curated library of 10k tracks sync'ed to my phone or streamed via Plex. Grown by CD purchases, or FLAC purchases from Bandcamp or else the best quality I can get from other download sources like iTunes or Amazon.

I think "burn-in" is mostly brain burn-in, where our ears/brain are adjusting to the headphones.

eh, not if he wants to fit his laptop monitor underneath like that.

Don't return them if you like them. Just buy some other closed backs and use the 660s when you're alone.

I have thousands of dollars worth of speakers. It's a colorful analogy. Calm down.

I have the 650s, the 599SEs, and I just finally bought the 600s - because they went on sale and I wanted to finally hear the differences for myself. To be honest, the 599SEs are damn good for the money. In fact, I did a headphone comparison with a buddy of mine (that's big into hi-fi and home theater but not into headphones at all) where I had him try about 6 pairs of my headphones. In doing direct comparisons between the 650 and 599se, having no idea what they cost, actually preferred the 599s over the 650s. The 650s warm sound takes some time getting used to them to appreciate their sound (in my opinion). For me it took getting a tube amp to sort of rediscover my 650s and appreciate them more. Something to consider.

I haven't done a good comparison to the 600s yet to form a solid opinion, but out of the box I think I like their sound signature better than the 650s too. But all this is very subjective of course. Seems like which one of the 6x0 series you like best is pretty much up to personal preference.

I have the XS, 600 and 650. XS are totally different - I wouldn't even compare them. I like both. The XS sound like I hung speakers from my head. Don't have anything else that sound like that. Very comfortable and easy to listen to all day. I was very curious about the Hifiman sound/lineup. Was super happy they released the XS, which by all accounts sound nearly as good (and some say better) than their more expensive counterparts.

Duct tape.

Hifiman Edition XS

(I imagine other Hifiman in that form factor may be similar, but the XS is what I have)