Tricked you! This isn't a review. At least not yet. However, there have been several requests for impressions of the mysterious HiFiMAN RE-ZERO, so I guess I'll go ahead and post a really, really brief summary first.
First, let me make it very clear that I received these earphones as a complimentary review unit from Head-Direct. However, that fact will not influence my judgement on the quality of these earphones, which are wonderful, nonetheless.
Packaging, Accessories, and Build Quality:
Let's start with the packaging. It's the exact same transparent case-like box that HiFiMAN currently uses, except with different stuff listed, of course.
Included with the earphones are a variety of tips, 5 pairs of filters, a clothing clip, and a mysterious adapter.
The HiFiMAN RE-ZERO themselves look and feel exactly like the HiFiMAN RE-0, but instead of being black, the RE-ZERO are in a shade of metallic gray, which I really like. They use the same cable and splitter as the current HiFiMAN RE-0, with one important exception. Instead of having a typical 3.5mm plug, the RE-ZERO uses a four-plate balanced 3.5mm plug, much like the plugs used by headphones with microphones.
This is a crucial market differentiator, as no other earphone, to my knowledge, uses this plug. However, natively, the balanced plug does not work with most sources on the market, giving either only one channel of sound or no sound at all. In fact, I do not have a single source (Apple iPod, Sony PCDP, SanDisk Sansa, iBasso DAC) that worked with the balanced plug. This is where the mysterious adapter comes in. It looks exactly like a generic channel splitter, but it's actually also a balanced to single-ended adapter, and it allows the RE-ZERO to be used with any source.
Okay. Let's get to the part you've all been waiting for. Sound.
As Fang said, these improve on everything the RE-0 has to offer. From what I have read, most Head-Fi'ers enjoy the HiFiMAN RE-0 but wish that it had more bass to offer. The RE-ZERO provides more bass, but doesn't stop there. I actually found the RE-0 to be quite thin, especially in the midrange. The RE-ZERO fixes that completely, by adding a smooth, "liquid-y" and detailed midrange. The excellent highs of the RE-0 are mostly untouched, but the RE-ZERO does try to balance the treble out a little, leading to slightly less extension, but allowing it to be much more natural and less sibilant.
Well. That's about it for now. I'll have a full review posted by next week!