Had a bizarre experience with the X3.
I was in a local "Amazon returns vendor" shop (not sure what to call it, but if you're familiar with the type of store then you'll know exactly what I'm talking about) and they had a pair of these essentially brand new in box for $65. I'm not the biggest fan of the X2HR so I didn't really think much of it, but I asked a clerk if I could open them up and test them.
He obliged and when I opened them, I saw the dual 3.5mm to 2.5mm balanced cable and I thought "Oh...that's actually a useful cable." I checked online prices for the X3 and saw that the pair in my hand was a great deal, so I bought it for $65 with the intention of keeping the 2.5mm cable for other headphones, and selling the X3 itself to basically get a free balanced cable.
So I get home and test the 2.5mm cable with a Hifiman HE6se I have on hand at the moment - only sound out of the left driver, nothing out of the left. Huh? (And my first thought due to uh...some past experience with Hifiman is that my HE6se right driver failed, but that's neither here nor there). Regardless, I also have a 400i on hand so I test the cable with that and yea, same problem. No sound out of the right driver. Then I thought "Oh, the X3 must've been returned to Amazon and ended up at the store because the cable is defective." So just to test if it was the cable, I hooked them into the X3 and ran it with a 4.4mm adapter through my Topping A90.
Now keep in mind, at this point I honestly had no intention to really even listen to the X3. I just wanted to see if the cable worked - and it did, which was strange, so I left the X3 on and listened while I looked it up. And yea, I found this thread detailing the very "interesting" decision Philips made with the wiring/cabling on these.
But as I did my research, I still had the X3 on going through a playlist and...uhhh, are these actually an awesome pair of headphones?
Long story short, I decided to keep the X3 after running them a bit more with a variety of genres, and also giving them a little EQ treatment. In my opinion these are absurdly underrated headphones in their price bracket (looks like it's sub-$200 on Amazon now). I'd even say, hell they might be my favorite pair of headphones sub-$400.
I did not like the X2HR at all and what I appreciate in the X3 is the presence of basically everything the X2HR's lacked. Where bass was boomy and uncontrolled on the X2HR, it is tight and technical on the X3. Tuning is neutral and not "Beats-fun(tm)" and don't get me wrong, there is nothing wrong with that. But in my opinion, in this price bracket it is actually really hard to find a headphone with great technical performance, very neutral tuning and a little bass lift just to give the low end some punch.
These are like ER2XR's with actual soundstage - which is the other thing, soundstage is great here, decent size and relatively airy.
With some EQ to my tastes, these X3 outperform many of my other, more expensive headphones on certain genres. Metal for instance is very fierce and crunchy with very little congestion. I honestly can't say if I even prefer metal on the HE6se over the X3, and the HE6se is notorious for being a godly set of cans for metal.
For me the X3 are superior to the 6XX, HE-400i, Sundara, Beyerdynamic DT990 Pro, and AKG K712 Pro. These are all the headphones of a similar price bracket that I currently have on hand and could directly A-B it with - there are many others that I think I prefer the X3 to, but I don't currently own them and I hate to compare between headphones based on memory. For reference, I rarely find treble fatiguing and my daily drivers are higher-end electrostats and an HD 800s, so maybe the X3 are just tailor-made for me except multiple price-tiers below my main setup. But regardless, I really dig them.
If you see one for a good price or even are willing to outlay about $200 for these, I'd say give them a try. They are a really great pair of headphones, terrible wiring/cabling decisions aside.