If you want full volume install Equalizer APO on SFX only (full guide in post 1
here), if you are using stereo and-or only 1 endpoint, disable the upmixer and secondary list.
You can add more devices as you go to each list, I isolate digital from analogue, so I use the top for Speakers-Headphones, bottom for SPDIF-HDMI.
The Realtek SFX has barely any features (other than upmix, which is now EAPO), so don't worry about disabling it.
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I also suggest the
CAudio fix to get best quality from E-APO, which uses restricted API.
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By default DTS:X Ultra runs in Music mode, however by default in Realtek, features such as environment are disabled. To turn off DTS, simply press the power button.
To edit the preset.xml, you may need to run PowerShell or CMD as admin then type notepad, this will open notepad as admin, so you can edit.
In my opinion, the DTS modes are much better than the Realtek ones, plus you can edit them.
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Note that off mode is not fully off, just no FX processing.
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SFX: Upmixing, downmixing, device volume (all channels), channel volume (independent), crossover.
MFX: Almost anything (EQ, so on) except upmixing. Most common effect point.
EFX: Speaker protection, other, encoding (DTS, Dolby).
Application >> SFX>MFX >> EFX | Only ever one EFX | SFX, MFX (per app).
RAW >> EFX | Only ever one EFX | No SFX, MFX, (per app).