[ubs28]

Since the Shure SRH 1840 are easy to drive, would an Apogee One be sufficient? 
 
If not, would the Apogee Duet be sufficient then? (since people also use the Apogee Duet to drive the much harder HD 650)
 
Does the Fiio E7 drive a Shure SRH 1840 good also?

 

[MalVeauX]

Heya,
 
The SRH1840 is very efficient. Anything discreet will drive it fine, with room to spare.
 
You should focus more on whether or not the sound signature/coloration is a good match, since literally everything will drive it well.
 
Very best,