Poweramp, another popular Android music player with high res support capable of bypassing the stack and interfacing directly with the hardware, also uses the SoX resampler within the FFmpeg decoder. Users consistently rate its sound quality as excellent.
By the way, the concerns about the stack are overblown when feeding it content at the native rate as no resampling would occur then.
Have you performed any double blind, level matched listening tests with which to base your assertments on? A spectral analysis of the exact same content with and without Android resampling at least? Because if one hasn't done that, well... it's just an opinion...
I'm curious about the open source software USB Audio Player uses also. I'd venture a guess that FFmpeg is part of it.