The point of Wasapi is to send bit-perfect output to your dac without the Windows mixer or anything else messing with it, so it will not work with Equalizer APO. However, if you use a parametric EQ plugin in Foobar2000 that will work together with Wasapi. I use the EasyQ plugin (it's a generic VST plugin so you will also need the Foobar VST
Audio amateur here. So Equalizer APO is a system-wide equalizer which supports VST plugins. Due to a longtime hearing condition which effects my perception of pitch, I have to pitch-shift/correct everything I hear on the computer -- roughly half a semitone downward -- so music and movies sound like normal again when using Netflix, Spotify, YouTube and stuff.

Equalizer APO won't work. Window 10. used to work after i reinstall my w10. I've disabled hardware acceleration and unchecked disable enhancement except for fiio sound setting there was no enhancement to select. installed as SFX/EFX. allowed it through firewall. I tried to delete registry but system wont allow me eventhough im on admin.

Turn up the volume a little and enjoy. At 0.0 there's not gonna be any clipping unless your source file has it. You're good to go fam no worries. You can also check the "prevent clipping" checkmark for it to automatically lower it. Then turn up the volume on your external amp to compensate.
And yes it's probably your other audio/video/etc. software interfering with Equalizer APO, I've seen that sometimes when people say reinstalling and so on don't work. As (Peace) Equalizer APO works fine for me with IEMs, headphones, AptX Adaptive USB transmitter dongles, etc. Try installing it on a different computer/device if possible to see
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how to check if equalizer apo is working