I've been liistening to Mojo with the usb connect for lg v20 for almost 2 hours since it arrived and i have to say i am pretty underwelmed with the performance.I can understand people being disappointed and saying it is not worth the money if phone is their only source.After changing again to coaxial and Cayin N6 and lowering the vol almost by a half (first green balls) the sound became much more open,much more clear,the mids are more fleshed out and not lean like with lg v20/mojo,vocals natural,layered detailed,bass much more depth and detail,it is pretty shocking actually.
I am pretty familiar with mojo's sound from coax as i've been listening to it for more than a year with the N6/dx90 so here is how i would rate the sound with HD660S.
Soundstage Width:Mojo/N6(good width taking into account that mojo does not excell in this area,very airy sound,very good space between instruments)>>Mojo/Dx90(a bit less width and air,enough space between instruments)>Mojo/v20(Not as open as the daps but a bit better than v20 alone,complex instrumental passages sound closed in and instruments mashed together)
Soundstage Depth:Mojo/N6(Very,very,good depth,sound is all around you,front and back,almost 3d,good layering,you feel like you are listening to medium desktop gear)>>Mojo/dx90(not nearly as good depth,less dimension to the sound)>>Mojo/v20(flat,2dimensional,no layers)
Mids:Mojo/N6(Very good clarity and detail,instruments are thicker and more realistic,vocals are awe inspiring,very open clear and natural,a bit to the front)>>Mojo/Dx90(Clear sound,detailed mids with the added sabre sound of dryness and analytical tone,vocals are clear but much less open and airy than N6/mojo)>>Mojo/v20(smoother mids overall,the sound is rounder,details don't scream at you as with the 2 daps,everything is a couple notches down,instruments sound lean,vocals recessed,not nearly as detailed or open)
Treble:Mojo/N6(Extension,airiness,sparkle,can be a bit fatiguing with sharp roll off,due to a bit of edginness)>Mojo/DX90(less extension and air but not as sharp)>Mojo/V20(Less air,sound is almost dark which surprised me as V20 alone is on the bright/analytical side,less extension but also less fatiguing)
Bass:Mojo/N6(Tight,very good detail and depth,very good balance but not very punchy)>Mojo/dx90(Slightly punchier but less detailed and controlled)>Mojo/v20(the punchiest of them all,on the dry side but less balanced and quality bass).
My opinion,mojo sounds better through coax than usb,more meaty and clear sound and scales much higher with quality dap rather than phone.