This depends on the fact that if the device being driven is an earplug or a highly sensitive headphone, it usually only needs 20% of the voice to listen to music (KA11 even needs less than 10%, so I don't think I need a device with more power than KA11). If the active speaker is driven, I usually adjust the USB dangle to more than 80% or even 95% (because some DACs will have greater distortion when approaching 0db), and then adjust the knob of the speaker amplifier to a comfortable volume. This can also avoid making loud noises when plugging or unplugging audio cables.
As for the audio format, I usually use Windows WASPI or ASIO drivers, so that the audio can be output according to the sampling rate of the audio file, rather than SRC to a fixed sampling rate. It is worth mentioning that after installing Fiio's ASIO driver, the Windows system's built-in WASPI driver cannot automatically adapt to the audio file sampling rate and instead has a fixed SRC to 48KHZ. Therefore, if you want to use WASPI, you need to manually replace Fiio's DAC driver with a USB Composite Device driver.