ThurstonX
Headphoneus Supremus
The other factor people need to remember about USB Audio Player (and Recorder) PRO vs. other Android audio players is that the former use a custom USB audio driver that bypasses the native audio chain in the device and shunts the digital signal directly to the attached (external) USB audio device. That's why it's possible to play hi-res (24/96, or whatever your USB audio device is capable of decoding) files with USB Audio Player/Recorder PRO. Unless you've got a seriously fancy Android device that has a built-in DAC with those capabilities (I've never read about one), you're limited by the built-in DAC and audio chain.