Yamaha RH5MA - Giant Killer. DT1350 performance level at 50$. However, much loser isolation and built.
SuperLux HD668 - Great price/performance, great build. Highly recommended for general use.
Takstar HI 2050 - Best price/performance I had ever seen. Good DT990 chineze clone. Highly Recommended.
HD555/595 - Good entertainment headphones, less good for music hobby, too boring and uninvolved.
DT880 (600 ohm) - Simply put, the best <300$ headphone I had. Reference performance indeed but hard to drive.
HD600 - Nice phones, but too slow and boring on most headgear I had pluged them in. Capricious and tricky. Sold
DT990 - Boomy but textured bass. Can't see any reason recommending these after having used DT880's or DT770.
HD650 - Unlike HD600, less boring, faster, less amp dependent. Highly Recommended.
K712 - My current favorite mid-fi headphone. Made me sell all sennheiser/bayerdynamic stuff.
T1 - Extremely hard to drive (1400 ohm pick impedance). Can make a false impression because of lesser headphone amp. Sounds good on speaker receivers. On it's best, beats each and every dynamic driver..
Headphone Amp Inventory:
LittleDot MKIII - after tube rolling pretty nice sounding and looking device. However it's noisy on high volume levels. (sold)
AMB M3 (sold)
Pegasus II HP DAC/AMP --> a great 300$ unit. I've sold everything previously owned and left this little device alone. No need for a dedicate amp, even a tube amp. Sound is neutral to warm, almost analog. Love it !
StereoLink SL 1610 DAC - nice 300$ dac, one of the best delta-sigma sound I've heard. Is it worth 500$, I don't think so...Sold..
AudioGD NFB11 - I'm glad i've sold it. Not particularly liked it from the very beginning. Ok, it isn't bad, but not as good as I've expected.
Audinst HUD-MX1 - ok, many guys like it, especially considering the price. I think it's a good sounding little device, but don't expect too much from it. It's too small to give us the big, HIFI-ish sound. I've enjoyed it anyway.
Creative X-fi XtremeMusic - If you ask me for a good budget soundcard - here it is. Great sound for only 60$.
Other Audio Equipment:
HiFiMan RE0 - to boring/aggressive on every hardware but HiFiMan DAPs. Can be moded very easy. Versatile after mod.
VSonic GR06 - Giant killer. Better overall built/accessories/isolation/SOUND then famous RE0
VSonic GR07 - better subbas performance and faster driver then GR06. Different signature, less warm, more sibilant.
Sennheier IE7 - very good value/money, baby IE8 for half the price, liquid-warm presentation, unlike GR07.
Sennheiser IE8 - huge soundstage, uncontrolled bas
Sennheiser IE80 - much better then IE8 in terms of bass control and treble energy
Sennheiser IE80 MOD - THY ultimate In_ear universal.