Ok,i narrow it down to these three.
All are close,all cost almost the same.
Which one is the best?
Looking for a detailed and neutral and natural sound,similar to Sennheiser HD800.
Which budget DAC & amp?
The 32-Ohm K550s and 42-Ohm SRH-940 would be best with a low impedance headphone amplifier.
(portable stuff is usually low impedance)
Where as the 250-Ohm T70s are great for receiver or a decent headphone amplifier and would be fine with a headphone amplifier that has a high output impedance (but a low impedance amplifier is just fine to).