Thank you for the answer.
English is not my native language.
I mentionned the chipset just in case.
If I understand correctly, you mean that an optical audio output is, like the analog one, affected by "some nasty Windows behaviours" ?
Regards,
Imagine you have a recording of Beetles"Help" stored on your PC's hard drive as help.flac. You want to listen to it.
You plug headphones into your PC and use a player like Foobar2000 to play it, but you don't want to use "Exclusive Mode" because you also want to use software to EQ it. Between the player and the headphones are a bunch of Windows functions (some are APOs). Some are native Windows, some come from drivers shipped with audio devices. You can't see them. Some degrade the sound a lot (e.g. by compression).
So you decide to buy a DAC and plug it into the USB port. BUT, these Windows APO functions sit between your player and the DAC plugged into your USB port.
So you decide to plug the DAC into the optical port. BUT, these Windows APO functions sit between your player and the DAC plugged into your optical port.
They are always there whether you use the onboard chipset, a USB connected device, an optical connection. You can bypass them by using Exclusive Mode on your player, but this can limit some control of some DACs and prevent you applying equalisation.
EAPO is another APO, that sits between your player and the onboard chipset, USB DAC or Optical DAC. It allows PEQ. It also has an option to DISABLE other APOs including the Windows limiter. This can have a very big benefit in sound quality.