Build quality, comfort, accessories wise it's true that the Superlux might not be as good. Sound quality wise?
There are always headphones with cheaper prices that are gonna sound better than the more expensive one, otherwise it would mean that the audio technology isn't improving isn't it?
There a reason why there's so much hype over their series of headphones despite being that
cheap because the sound quality truly shines. I haven't heard of any of their products but there are strong, solid positive reviews out that that's enough to prove that the sound is good.
Allow me to quote some of the audiophiles maestros out there:
QUOTE(Mike from Headfonia)
All in all, the HD668B is a kind of headphone that “wows” you the first time you hear it, particularly because of two things: its exceptional sound and its price tag. Compared to the Alessandro MS1i, the HD668B sounds clear, spacious, everything is well-placed, and more natural, while MS1i sounds compressed, right-on-the-face, and not as clear. The MS1i just doesn’t have the HD668B’s impressive balance, acoustic imaging, and clarity. And at a mere $30, this headphone definitely competes with those that are priced two or three times as much, in terms of price-to-performance ratio.
QUOTE(|joker| from Head-Fi)
Sound (8.25/10): Putting aside all criticisms of the HD668’s derivative styling and consumer-class plastic build, what’s left is the sound quality. The drivers Superlux crammed into the 668B are very, very impressive and no sub-$80 headphone I’ve heard before sounds quite this good. The general signature is balanced, crisp, and neutral in tone. The bass not at all exaggerated, instead appearing tight, quick, and accurate. Technically, they extend quite low but bass notes really thin out below 50Hz and the typical bass ‘rumble’ present in many consumer-class headphones is just not there.
Value (9.5/10). (MSRP: est. $60; Street Price: $50) The Superlux HD668B has been praised plenty as of late, and all I can do is just heap it on – for the asking price, the headphone is an incredible performer for those who put resolution and clarity above all else. If there’s anything questionable about these, it is their portability– while they don’t look as bulky as my AKG monitors, come with a portable-length cable, and play nice with battery-powered sources, they are still full-size cans that don’t fold and really aren’t built to be crammed in a bag. For portable use, the similarly-priced Beyer DT235s may be a better choice with a well-balanced sound signature. For use at home, the HD668Bs sits atop the competition.
Now, what I'm trying to convey isn't about how perfect Superluxes are and how good they sound compared to those two/three fold the price, just trying to tell that don't mistake it for some Mix-Style headphones. In the case of Superlux it is just hard to accept the fact that despite being this cheap, the sound quality is unbeatable. They replicate designs, they look cheap and seems to be built cheaply and the price is cheap - but the sound isn't.
Disclaimer: I'm not working for Superlux nor I own or have any plan of owning one in the future, just telling my experience of reading reviews

But when you see me recommending Brainwavz products do take them with a graint of salt because I'm already addicted to them