I just ordered a 650 last night from bhvideophoto for $313.99 flat. At the time i thought it was a good deal but I'm not so sure anymore. I wanted them because I thought they were a big step up from my 598s, but after looking at some reviews, many say that the 650 is boring and the 598 is more engaging.
Update: I plan on using them with a Cayin C5 portable amp.
I've not owned the 598.
Think I came across the similar 'criticisms' of the HD650 when I was perusing amazon a few years ago. I didn't have much interest in headphones then, and the price at the time of around £370 put me off.
Having purchased them and owned them, I have to say those reviews saying that the HD650 being 'boring' is an accurate description, albeit a slightly clumsy one. It doesn't have exciting emphasised bass or treble. It sounds pretty even to me, and hence 'boring' or understated. Understated sound gives you flexibility in listening to any genre of music, which can't be said of the W1000X/W5000. It's not hyper detailed like the T1 but it is plenty detailed. This smooth sound also gives long term listening comfort, and longevity in appreciating music and the gear, as opposed to being initially wowed, and then tiring of the sound signature.
Some will find the HD650 boring and dislike it. Sometimes, even I find it stuffy, lacks the openness or airy sound that I desire. But then those same ears can't get enough of its tone during a long night listening session. So contrary to what many in this forum state,
I do not trust my ears. I therefore like to give any headphones the time to adjust, and each find their place.
TL;DR: I don't see 'boring' as a criticism.
I've not used the C5, but I find the HD650 are pretty easy to power. I use it with the microstreamer when I'm on the laptop, and they sound almost identical to my desktop rig.
IMO and YMMV as always
edit: typo
