fridaythe13thpreySkip the Fidelio X2, as their sound (and potential) is a significant downgrade from the HE4XX. If you don't already have one, I highly recommend that you purchase a balanced DAC/amp (like the FiiO Q1 mkII) and a balanced cable. Using a custom EQ profile and Brainwavz XL protein leather earpads will also improve the HE4XX's sound. Let me know if you would like to know more.
mattristhank for the info. i currently using fiio e10k . but it seem not enough to push the volume level to my liking. should i get a seperate amp for 4xx. i also have little bear b4 to power my m50x. but little bear having some distortion issue with 4xx on high volume. should i get an solid amp over tube amp? i m currently eyeing on topping a30. will it be sufficient? or should i change to a better dac/amp combo
fridaythe13thpreyYeah, the 4XX requires significantly more 'juice; ' than the e10k can provide. I run mine with a FiiO Q1 mkII using its balanced-out, and the sound is noticeably cleaner than using its standard headphone jack... and can be driven louder. This is the cheapest way to make these headphones 'sing'. Plus it's portable and is plug-and-play with iOS devices (iPhone).
If you decide to go this route, make sure that the plugs that feed into each earcup of your headphones are 2.5mm... which should be visibly smaller than the 3.5mm 'headphone jack' end. If they are, I recommend getting this balanced headphone cable: https://www.ebay.com/itm/Silver-Plated-Cable-for-Hifiman-HE400S-HE-400I-HE560-HE-350-HE1000-V2-Headphone/223042745518?ssPageName=STRK%3AMEBIDX%3AIT&var=521897782022&_trksid=p2057872.m2749.l2649
... for $20, and it will be shipped to you from China in about 2 weeks. If you don't want to wait, similar (more expensive) cables are available Amazon (Prime-shipped). Once you have the Q1 mkII and balanced cable, let me know, and I'll give you an EQ profile that will remove the 'haze' from the sound. (If you want, you can find it in the 4XX discussion. Just search "APO".)
One final thing: Would you be willing to exchange the 4XX earpads for ones that are more comfortable and/or improve the sound even further?
fridaythe13thpreyIt's unbalanced-out is not nearly as powerful, but you'll have no issue powering any 150-ohm (or less) dynamic-driver headphones. Sound quality-wise, it has no match for a small DAC/amp at its price-point. (From a direct comparison, I can tell you that it sounds significantly better than the Micca Origen+.)