Euphony includes HQplayer embedded installation. HQPlayer embedded contains most of audio processing capabilities of HQPlayer Desktop application.
From HQPlayer site:
“HQPlayer is a high quality audio player for Windows, Linux and macOS. HQPlayer also features several selectable high quality upsampling and downsampling algorithms as well as selectable dither, noise shaping and modulator algorithms.
All modern DACs employ oversampling and delta-sigma modulation, however the hardware implementations are more or less resource constrained. Higher quality oversampling and delta-sigma modulation can be done by utilizing vast mount of processing power available in modern PCs. Many AVRs also resample internally to 48, 96 or 192 kHz, with the HQPlayer, these can be fed at the native rate.”
In second case, when enabled in Euphony Settings, HQPlayer will play all songs inside Euphony Stylus queue with exception to songs that HQplayer does not support (i.e. mp3 songs). The songs that HQplayer does not support will be played by Stylus player.
HQPlayer is included because of great up-sampling capabilities that it provides. If you don’t need up-sampling then it’s best to just use Stylus player.
For HQPlayer embedded capabilities and settings refer to HQPlayer site