Shure 1540 has spec:
Sensitivity 99 dB/mW
lmpedance 46 Ω
Frequency Range 5 Hz – 25 kHz
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I think not really hard to drive, portable DAC/Amp like DragonFly or Audioengine D2 ( I have this ) will able to drive the Shure 1540
Threre are other altenative as well like DACport. It's better if you can audition before decide which one macth for you.
Good with your choice..
~ron~