Introduction to the HiFiMAN RE-600 In-Ear Monitors
After reviewing the excellent HiFiMAN RE-400 Waterline in-ear monitors (earphones), I was graciously sent the RE-600 Songbird, a higher-end model offering better performance, for a price. At $399, the RE-600 are a serious investment into music playback and more than most want to spend. My conclusion is that yes, the RE-600 Songbirds are indeed worth the higher price tag. Find out why and just how much of a difference there is between the two in my review.
HIFIMAN RE-600 IN-EAR MONITORS
SPECIFICATIONS
Design: In-Ear Earphones
Drivers: Titanium, Dynamic
MFR: 15 Hz - 22 kHz
Nominal Impedance: 16 Ohms
Sensitivity: 102 dB/mW
Weight: 0.48 oz
Price: $399 USD
HiFiMan
SECRETS Tags: HiFiMAN, Earphones, Audio
Design of the HiFiMAN RE-600 In-Ear Monitors
The design of the RE-600 is nearly identical to the RE-400. They both utilize the same aluminum housing with the only difference being the gloss black finish on the RE-600. The insides are where the two models differentiate themselves. The Songbird's driver has a patent-pending coating on the titanium driver that they claim extends frequency response and enhances detail. The RE-600 also uses a composite coil whereas the RE-400 makes use of a standard copper coil. 
To round out the differences between the RE-400 and RE-600, we get a slightly thicker cable made from copper and silver as opposed to only copper in the RE-400 and at the end of the RE-600 cable is a balanced 3.5mm mini plug. This balanced connector only works with compatible devices like the HiFiMAN HM-901, but comes with a 45 degree 3.5mm plug adapter just like on the RE-400. The cable is sheathed in a mesh material that reduces the cable's urge to tangle. Some might complain that there are no in-line controls for use with a smart phone, but I personally never use said controls, so it was not a drawback for me. 
The packaging for the RE-600 reflects the premium price point with an elegant design that folds out to reveal the in-ear monitors and an assortment of earpiece fittings. Included among the various sizes of silicone ear tips are a couple pairs of Comply foam tips. I went straight for these as I usually do not do well with the seal provided by silicone tips.
Since the fit is essentially identical to what I covered in my RE-400 review, I won't waste too much time on that. My quick conclusion is that the light weight and small size of the HiFiMAN in-ears make for a very comfortable listening experience. I have yet to have issues with the in-ears falling out, or pushing uncomfortably against my ears. This is one of the most comfortable in-ear designs that I have come across.
The tonal balance of the re600 is fairly neutral with some midrange enunciation. Vocals have a little more body to the presentation but never sound throaty or muffled. The high end detail was crystal clear and bass was quick, taut, and solid but not over powering. These are not bass whores nor are they thin and empty. I found them to be right in the sweet spot for me in terms of bass quantity.
On the venerable classic, Kind of Blue by Miles Davis, the RE-600 Songbird absolutely… sung! I hate to take away from the incredible value and performance of the RE-400, but if you want the depth and dimension of well-reproduced sound, then it does take a little more investment. The difference is immediately clear when comparing the two in-ear monitors with how they each present the soundstage as a whole, as well as with individual instruments. The RE-600 gave a much greater sense of depth. The echo of the instruments appeared on a different plane than the instruments themselves. The saxophones took up a space of their own on stage, like there sound was modeled in a cube as opposed to a flat piece of paper. The bass on the RE-600 was both cleaner and tidier. The midrange had a bit more body to it that really stood out when the solo instruments reached peak levels. High end detail was excellent, offering a wonderful tangibility to the sound. The RE-600 did an excellent job at recreating the feeling along with the sound of instruments, such as the strike of a cymbal by a drumstick. I not only heard, but in a subtle way, felt the metal clink followed by the misty metallic shimmer of the cymbal vibrating. The added tangibility from the RE-600 was easily worth paying extra for.
The piano sound on Michael Nyman's soundtrack for The Piano was full, robust and planted within the soundstage. Aggressively hit notes rang with each impact, showing off the dynamic capabilities of the RE-600. The saxophones had a lush sound that, although not quite as forgiving as the RE-400, was certainly more detailed and in the end, a more enjoyable experience on the RE-600.
I think paying extra for the RE-600 Songbird is a lot like going for a prime cut of aged rib eye over a select grade cut of beef. Sure the select grade steak will taste pretty good and fill you up, but you miss out on the tenderness, juiciness, and butteriness of a well-marbled prime. If you want more dimension and tangibility to your music reproduction, the truth is, it costs extra. Opt for the RE-600 Songbird over the RE-400 Waterline if that is what you are looking for and I highly doubt you will be disappointed.
HiFiMAN RE-600 In-Ear Monitors Rating
Looks: 
Build Quality: 
Comfortable Fit:
Sound Quality: 
Value: