Linux

Check out Pipewire, which is the modern standard of linux audio

I do not have the same requirements than you, but in audio production I can route anything in any which way I need (useful for switching monitoring or sources), and I did once plug an eq to my movie player because some ripped movie was really sounding bad

There are tons of VSTs available, too

There'll be research to do, and a learning curve, but today is not the days of Jack anymore, it has become really easy if you go for a modern distro (arch, tumbleweed, fedora,...)

Have fun running your sound your way!

If you want to patch your programs that process your input and outputs audio you may want to look at pipewire + https://gitlab.freedesktop.org/rncbc/qpwgraph

Pipewire has built in EQ support (no GUI, but useful once you've chosen your settings), and you can use EasyEffects for a GUI to experiment with.

Pipewire also supports complex multichannel impulse responses (including the same files that Hesuvi supports if you supply them). Both of these are a bit challenging to configure it should be said, but it's nice they they are just effectively outputs you can connect to once they are setup, and don't require a bunch of programs running at once.

Here's the official example for virtual sound with "hesuvi": https://gitlab.freedesktop.org/pipewire/pipewire/-/blob/master/src/daemon/filter-chain/sink-virtual-surround-7.1-hesuvi.conf

I've had issues with relative paths in the past for the filenames, so try setting a full path if it doesn't work.

And here's an example for EQ (you can add more channels if you need them): https://gitlab.freedesktop.org/pipewire/pipewire/-/blob/master/src/daemon/filter-chain/sink-eq6.conf

You can also add a preamp if your EQ needs that which is just essentially a 0.0 freq, 0 Q filter and then you set the gain that you need. I didn't need it as I'm not using external amps for any of my pipewire EQs.

One more thing I'll add is that if you want the effect to also connect to a specific output (maybe your headphone EQ goes to one output, and your speaker EQ goes to a different one) you can set target.object=<your hardware output> in playback.props section. There's an even better solution in wireplumber 0.5.X but I haven't tried it yet and it might not be available on your system. Read this Collabora article if you're interested.

Not sure how much of your ground it would cover, but I've used easyeffects in the past to apply noise cancellation. Worked very well. It's also on pipewire level so you don't have to mess with alsa directly.

I do recall it having many more plugins as well as eq, I just didn't have a reason to use it.

I second the comment about pipewire. There are graphical utilities that can help with routing. Take a look at "qpwgraph" for that. It is set up kinda like a puzzle, but once setup it restores your prevoius set ups. The initial setup can be a lot. Especially since it fights the default audio settings of your distro. But in my experience not as much as windows. It only does routing though. There is no volume setting, muting, etc. That still has to be done via the regular sound settings.

Now I believe voicemeeter has functionalities for gates, compressors and other effects. I have tried easyeffects recently and... well it works. But it can be tedious in combination with qpwgraph. None of this is as streamlined as voicemeeter unfortunately. But I admit that may also be due to my own incompetence.

If you were using the vban utility of voicemeeter, there is a linux version on github, which you need to build yourself. It is commandline only, but the protocol is the same and it is high quality realtime audio streaming in your network. It works well in combination with qpwgraph.

https://ubuntustudio.org/