Have you found an answer yet? I have tried over and over and still I'm getting that error.

I will share what i did to get eq working in Antergos.

1. Copied eq1 folder to linux
2. removed files from eq folder as per p99 website
3. When copying p99 specific files into eq folder pay attention to case sensitive files, in particular dsetup.dll! You have to rename it to DSETUP.dll
4. Get sound to work. Open terminal and enter sudo pacman -S lib32-alsa-lib lib32-alsa-plugins lib32-libpulse lib32-alsa-oss lib32-openal
5. Edit eqclient.ini and change video mode or size to fit your monitor
5a. Change windowedmode to false if you want fullscreen
5b. set refresh rate to 60

Is there a way to automate casechecking? This is painstaking, mind-numbing work and there's no guarantee I'm going to get all of the mismatched cases.