As title said.
I love HM-602 DAC. It beats HDP, Sparrow, Pico DAC/Amp, D10. It does provide musical sound, which is closer to analog, namely to tapes / cassettes. It also does not give up to the DACs mentioned above in summary of technical terms. I mean specific SQ terms, taken by ears, not measurements.
I bear with HM-602 amp. It is good enough to not hassle with most of the portable amps. I compared it with Meier Move, which is one of the best portable amps I tried. Headphones were HD-650, RE262, KDE250, PortaGold and KSC-35km - last two are my deep modded Kosses. Music was various. Move was better in most cases, but not better enough to carry bigger brick around and to worry about batteries. HM-602 sometimes was passable, sometimes had excellent synergy, say with Kosses.
I like the resulting sound. This synergy with Kosses sounds like HiFiMan tried to reproduce 80's portable sound, say Walkman > PortaPros. Well, the mission complete and I respect the results. I grown up on this sound and I always feel myself comfortable with it. It is kinda "Back home, baby. Welcome back to 80s". I am still interested to climb higher on SQ, but HM-602 shows me the right direction now.
I can hardly tolerare HM-602 firmware. Using HM-602 buttons, it is really possible to develop UI same to or better than Sansa Clip UI, which is miles ahead.
I hate HM-602 informational support. I bought $80 Class 10 SD card just to learn it does not work. Customer support replied quickly - yes, it does not work, but Class 4 works. They knew this and they still did not added this info on to official product page at head-direct.com. It is a shame.
So, what is a summary? See my sig. If HM-602 is still there, then it is still a winner, despite its flaws. It presents one of the best combinations of SQ, portability and functionality up to date. It provides the best SQ among all the portable DAPs I tried, including all iPods, all Sansas, some Cowons, Sonys and HiSounds.
I respect what HiFiMan (Fang) does for our hobby. This product is another great long-awaited gear for head-fiers. Unfortunately, there are some major things to improve aside of sound quality. I hope my review will help Fang to make customer satisfaction even better. Some things, like public info on product incompatibilities, a very easy for vendor to improve. At the same time, they are critically important for customers.
Update Feb 20, 2011: I love it, it is incredibly great. It makes portable amps pointless and has a nice synergy with HD650. It is the best player I ever owned and the last I ever will part with...
... until it plays from my laptop USB. Unfortunately, it adds clicking noise. It requires a powered hub to play right. I yet to solve this with a customer support.
Update Sep 23, 2011:
It works well from USB with USB hub, even if no external power is used, just PC > Hub > HM-602. I found small hub and now can use USB with comfort.
I prefer to add Meier Move to amp HM-602, when listening HD650. HM-602 amp is evidently colored, sometime this is for good (with RE272), sometime not (with HD650). Move is much better with HD650.