So I did a bunch of A/B and critical listening today. For reference I am a nearly 38 year old male who has previously reviewed professionally and have heard many high end home theaters. I tested my hearing and can clearly hear to at least 18.5kHz and have no issue at all picking out lower bitrate mp3s. I also own RHA MA750s, SHure e4s, Grado SR80s and a few others, but really haven't been much of headphone guy.
Comparo one: Schiit Magni/Modi, foobar HE-400 vs Fidelio X2. Mine are the X2, friend has the HE-400, flat EQ. As expected, right off the bat we both "liked our own", but he admitted the X2 sounded more like how he likes his bass (he normally has a bump centered at 60Hz). Also his immediate comment was that the X2 sounded like large speakers with bass capability, not a speaker with sub.
The HE-400 is actually too flat in both our opinion for bass. I suppose you could say that makes it audiophile grade - but that isn't how it sounds in high end speaker setups, well set up concerts, etc. The real world isn't flat. I thought the He-400 was bright and a bit forward, but again, I have a brain bias from more hours on the X2. He-400 has more upper end air and treble (a bit edgy for me), good detail. I can't clearly state one is better (even though I vastly preferred the X2...not even close), they are just different signatures.
Comparo two: My dedicated Home Theater (HT)....SVS PB/2 ultra sub, EQ'ed to listening level within +/-3 dB for 20-120Hz, crossed over at 80Hz, speakers are Rocket RS-850s, Denon 4306, running in stereo (plus sub, set to +2.5dB hot)....vs the X2. AudessyXT EQ processing and room correction (distance corrected, proper spacing and toeing as well). What struck me was how similar the two sounded....like exceptionally similar requiring some repeated A/B. This, my friends is a very good sign.... I proceeded to test a few of my favorite tracks. Mark Knopler's shangri-la was first up. X2 vocals were more pleasing, a bit more forward. The HT did have a slight advantage in air, and definitely in instrument spacial placement, it is almost 3D (height depth and panning). Overall pretty close - but the good stereo system won out for "putting me there" it just sounded more like an intimate concert with Mark on stage. That said - the X2 revealed certain things (especially vocal tonality) that the HT didn't.
On to track 2/3. AD/DC Thunderstruck and Fire your Guns (both off Razors Edge). This wasn't even a contest...X2 won hands down..capturing the kick drum slam, no edginess at all, stunning. My HT struggled with some edge to the cymbals and secondary vocal tracks on Thunderstruck.
Final track - Dave Matthew's Crash. Really tough call, but again I go to my HT with the edge for putting you there. I think I found my first "flaw" in the X2 after repeated listens (over and over....) some of the cymbal decay wasn't perfect, I could tell it was a cymbal and without A/B I thought it was amazing...but the HT captured it perfectly..it sounded exactly like it was a real cymbal. Similarly the snare taps...the rattle of the snare was just the tiniest bit off of the HT...which admittedly is almost perfect in this area.
Final thoughts on the comparisons. I came away more impressed than ever with the X2. I realized I was giving my friend's He-400 the benefit of the doubt (because of brain conditioning favoring the X2)...the reality IMO is that is just is outclassed for most of the audio spectrum. The X2 sounds like a very good speaker set up in a room...surpassing my own in many ways, falling a bit short in a couple (some due to physics...you just can't create a perfect stage forward of you). I would say the X2 is right around 2-3 dB "hot" on the lower freq vs mids....just about perfect and aligning with normal bass gain of speakers in a room (sounded like mine with a 2.5dB sub gain). I have listened to music on the X2 since I bought them with a fervor I can't remember, almost like an addiction.
So TL;DR: The X2 competes on many fronts with my many $k home stereo, and in my opinion, really outclasses the He-400 as far as sounding like a good stereo speaker setup / intimate concert. These are my opinions, nothing more. The X2s have a bit of warmth I find exceptional for longer listening periods while still capturing every detail in the upper end. They do lack (or give up as a compromise?) just a bit of air which also surfaces in a cymbal or snare decay. I am exceptionally happy with this purchase.