Just wanted to follow up with my initial review since I got a chance to use these headphones more and to compare it to my other Bluebuds X, Tone+ HBS730, Klipsch S4A II, and even pairing it up with Antec bluetooth receiver to make it wireless. My comparison was purely from a sound perspective. The reason why I did that was because I realized in every review I comment about one or the other sounding better than previous pair. But it's always a relative comparison. A new pair of earphones sounds great up until you compare it to another one.
If I have to rank them in order of sound quality (price and wired/wireless aside) it will definitely be:
1) UE 600vi (not as deep bass, but very balanced and natural, and some of the cleanest mids/highs I ever heard - brings music to live)
2) Klipsch S4A II (bass is deeper but still clean, mids are ok, but highs feel rolled off in favor of bass enhancement)
3) Bluebuds (bass is deeper, but also feels a bit muddy, mids/highs don't sound as natural/clear - probably internal processing enhancement/compensation)
4) HBS730 (lack of bass, and over-exaggerated mids/highs, sounds harsh and not natural at all).
Also when using UE600vi with Antec bluetooth receiver, sound becomes more compressed and looses lows and top highs probably due to bandwidth limitation of bt transfer. It surely becomes convenient since you can use these earphones wireless now and get the full control of playback and volume from the attached receiver. But the only way to keep these sound naturally, you need to have a direct connection to the phone.
Another things I forgot to mention is a brilliant sensitivity of these headphones. Typically quality earbuds will have 100-105 dB SPL/mW, which means the sound is not as clear at low volume and you really need to crank it up where in some cases when it gets loud the distortion happens. These are 115 dB SPL/mW which means the sound is loud and clear even at low volume setting and you can crank it up loud with very little distortion. I never been an audiophile, but once you start comparing and appreciate the sounds, you want to learn more about it