So these are the steps I took:
1)Download the HeSuVi .exe and extract it.
2)Download the 7.1 config file mentioned in the pipewire filter-chain wiki page
3) In that file, changed the "hrir_hesuvi/hrir.wav" sections with the full path to the atmos.wav file which I got from the HeSuVi exe.
4) Put that file in ~/.config/pipewire/pipewire.conf.d, alongside pipewire.conf
4)Restarted pipewire, pipewire-pulse and wireplumber services.
5) Went to pavucontrol to change the output.
So now when I play the test surround file supplied by HeSuVi with mpv, there is a huge difference, except, it is basically mono, I think. Without all the virtual surround stuff I am at least able to separate the side/front and centre channels, and if I concentrate I can separate front,side and rear. However with the virtual surround enabled I cannot pick out anything, even left and right. However, I can hear the .1 channel’s bass which I cannot hear without virtual surround.
So I was wondering if there is anything else I have to do.