The Nexus 5 audio output is average and has below average crosstalk. http://www.gsmarena.com/lg_nexus_5-review-1011p7.php I still use my iPhone 4s, as there hasn't been an droid that my (multiple) IEMs don't pick up a hiss on. :( Tried S3, HTC One, and nexus 4. About your bass problems it may be related to output impedance of these devices, i dont know what the output impedance of the nexus 5 is. However the HTC One has "beats" enabled, which is just bass EQ.
11/14/13 at 1:30pm