So, i've been listening a lot to both of them and have found out that the soundstage makes a very big difference in perceived sound quality. Here's a few pictures of what i hear.

 

While it is not always the case, i' believe these could be called their "native" soundstage.  I feel like X2's sound surrounds you, wraps around your head and sings. You have a much needed space in the middle, and music is further away. HD650 sound originates in your head, between the cups and there is no room for "you", the centre of head is mainly occupied by in-your-face vocals, like the singer is singing half an inch away. I listen my music at around 70dB, but for testing purposes i cranked that up to 90-100dB. On HD650 the vocals basically took over the song, and started to sound piercing like my friend has mentioned. I could crank up X2's to infinity (not really) without feeling anything like that.

I also found out why HD650 sounded better when switching the music. On some tracks X2's soundstage shrank to HD650 level, and then the latter has a field day. When X2 soundstage is small like sennheisers it sounds too fat, it cannot perform good if crammed in small space. The worst is when i listen to hip hop - X2 is just awful. Overly warm, bassy nightmare. Two examples where HD650 destroys X2 (i have high quality source of them):





X2 destroys HD650:


I believe X2's have a leg up on certain tracks over HD650 not because of the bass or the fun factor, it's because of the soundstage. I cannot understand why such narrow soundstage, for an expensive can like that, is accepted as normal. No one talks about this issue. Before buying, i haven't read anything like this. HD650 is not a closed can, and i'm not saying it sounds like one, but it should be definitely its forte as an open HP.

Obviously i'm not an audiophile, and this may sound very stupid for all i know haha. But i challenge your recommendation for a "budget audiophile headphone". It should be X2, which is cheaper by itself, and doesn't even need 200$ dac+amp to achieve comparable sound.

the Senns which are more linear and with less than ideal power need to be cranked up making more flaws obvious

This definitely makes sense.

How are you coming to your 90dB figure btw? Do you own an SPL meter?

Haha no, the best i could do is use an app from a smartphone and shove it between the cups. I know it's not ideal but the main take from that was harshness on vocals when cranking up the volume.

Th 6xx is not an entry level recommendation. It is a mid-fi to even top tier recommendation for people willing to drive it well and use good sources. It was never recommended as a headphone that can sound best from your iphone like an x2.

HD650. Schiit Magni + Modi. $99 + $99. No kidding. No schiit. No risk other than shipping costs.

Sounds like a budget build suggestion to me, otherwise you'd recommend to return HD650 if someone's not ready to spend serious cash to drive it. I would argue that two times cheaper option is definitely a better buy while getting arguably better sound.

Also, just watched Tylls X2 review, and at the end of it he basically said that X2 is a better buy if you dont want to invest on very good dac and amp. Someone said a few pages ago that this is the guy to trust.

I believe X2's have a leg up on certain tracks over HD650 not because of the bass or the fun factor, it's because of the soundstage. I cannot understand why such narrow soundstage, for an expensive can like that, is accepted as normal. No one talks about this issue. Before buying, i haven't read anything like this. HD650 is not a closed can, and i'm not saying it sounds like one, but it should be definitely its forte as an open HP.

Obviously i'm not an audiophile, and this may sound very stupid for all i know haha. But i challenge your recommendation for a "budget audiophile headphone". It should be X2, which is cheaper by itself, and doesn't even need 200$ dac+amp to achieve comparable sound.

I'm not sure where these "closed can" "narrow soundstage" issues speak is coming from. An HD650 is not a closed sounding headphone even from my 2i2 or indeed the headphone output of my POS laptop.

If you were complaining about bass being un-refined or sub-bass, I would understand.

Furthermore, your X2s are about the same price as an HD600. So, I'm not seeing the budget improvement.

For lower impedance, and much lower $ get an HD558 and even then I would be surprised if your X2 did better than that.

I have an AKG K7xx with me that sound more "alive" I guess. But soundstage is shit out of every headphone I've heard with the exception of a pair of cans driven by the Realiser which indeed fooled me into thinking sound was coming from the freaking wall in front of me.

Differences in how we perceive stuff are more understandable to me if we were talking about IEMs. But these are full size open cans. I'm more inclined to believe that you just like a particular coloration and are a bit confused about soundstage.

This bass in the back, strings on the side and vocals in the front from an X2 sound like complete BS to me. Frequencies in strings overlap with vocals. Even drums have mids. So you would hear sound from drums partially coming from the back and partially from the sides. Vocals have somewhat different ranges. I mean, if what you say is true, the X2 is a complete cluster fuck.

Well, there was talk on the X2 making the Leaderboard a few week back. It was pretty close, until I personally decided to nix it. Your (foxfluent) arguments have almost convinced me to reinstate the X2 perhaps on a conditional basis. My reasons for nixing the X2 as Leaderboard material were as follows:

• Decent frequency response, but not quite there. As I mentioned earlier. A bit of boom. A bit of tizz. A huge priority is good frequency response with smooth transitions.
• Not as scale-able as HD6x0, etc. Ultimately lacks resolution, bass quality, and dynamic slam of the HD6x0 with better gear. Yes, the X2 is a good headphone if we don't plan on upgrading DACs and amps. However, this is Changstar, not CNET. We expect people to move up. Scale-ability is an important factor here. Not having a enough good chain is usually the #1 reason for divergence of opinion of gear between here and other sites (this is something that should be discussed more.)
• The X2 with its greater distance of drivers to ears and slanted baffles, provides an immense sense of open space. While soundstage is an important factor, it has never traditionally been a top factor here. Take for instance the T1 which was soundly rejected despite its expansive soundstage. The motto kind of goes, if you want soundstage, get speakers (or the HD800).