What Serento does to your audio (nothing)
Serento is a control point, not a player. The audio never passes through your phone.
Serento tells your streamer what to play and where to get it. It does not carry the audio itself.
The stream travels directly from your server to your renderer. Your iPhone, iPad or Mac is out of the path entirely, which is why locking the screen, switching apps, or a weak Wi-Fi signal on the phone does not affect the sound.
Nothing in Serento resamples, re-encodes, applies DSP, or touches the bits. There is no equaliser and no software volume stage in the audio path by design. When you change volume, Serento asks the renderer to change its volume; if a renderer reports no volume control, Serento shows none rather than faking one by scaling the samples.
The one exception is when you deliberately choose your own device as the output ("This iPhone / iPad / Mac"). Then Serento is the player, and the audio does pass through it.
Still stuck
Write to us with your server, your streamer and what you expected to happen. If you can, send the diagnostic log from Settings, it usually answers the question faster than a description can.