While the iPod nano doesn't get everything right, it nails many, if not most, of the important bits (pun!) necessary to play your expensive earphones and headphones back really well. Follow the below link for full RMAA results of the iPod nano 7G running various loads.
RMAA: iPod nano 7G various loads
RMAA summary: AK240, DX90, MD-DR7, & iPod shuffle
The above is a summary for the RMAA tests of the following devices:
Astell & Kern AK240
iBasso DX90
Sharp MD-DR7
iPod shuffle 512
All tests were performed with the same input hardware, a lowly Edirol FA-66. Volume outputs were matched to within 0,5 dB. These are unloaded scores.
(BTW, I like the AK240 more than I care to admit.)