[Android Apps and Games] oscillum:
Sadly it still won't work for me. Would you mind sharing your procedure, or did you simply install the drivers and reboot without AML etc.?

EDIT: SOLVED

I finally got it to work on my Galaxy S10+. Poweramp, Spotify & YouTube all work with Legacy Mode enabled.

I'll share my specs and steps in case somebody encountered similar problems on a similar device.

Phone

Samsung Galaxy S10+

Android 10

SELinux Enforcing

Magisk

Magisk Manager v7.5.1 (267)

Magisk v20.4 [from Custom Channel]

Modules

ViPER4Android FX v2.7.2.1 [installed directly from within Magisk*]

(* The app itself did not install while flashing. It had to be installed manually from Internal Storage\ViPER4Android\v4afx.apk)​

Audio Modification Library v4.0 [installed directly from within Magisk]

Riru (Riru - Core) v21.3 [AFAIK this is not needed for V4A]

Riru - EdXposed v0.4.6.1 (4510) (SandHook) [AFAIK this is not needed for V4A]

Procedure

DISCLAIMER. I'm not all too deep into this. In the last few days, I tried various procedures at my own risk, encountering bootloops and having to reflash my system on the way. So, at least have a BACKUP ready (I personally use Titanium Backup, I do not have TWRP).

I will not be held responsible for data loss or damaged devices. I'll help where I can. If anything needs clarification I'll try my best, and I may also provide you with files/outdated versions. But don't expect any magical fixes from my side if something goes wrong or does not work.

Sidenote: In the above specs, I included Riru and EdXposed simply for the sake of completeness. Both Riru and EdXposed have not been altered during the process, meaning they were working for me before, and also do now after I got V4A to work. They did NOT work when I removed Magisk Manager and "updated" (read: downgraded) Magisk itself from the custom channel, but after the final reboot they both worked like nothing happened (luckily). Needless to say, EdXposed Modules also worked (i,e, GravityBox [Q]).

Be sure to remove any previous V4A as well as Audio Modification Library installations you may have and reboot your phone before you start!

Uninstall Magisk Manager [in my case Magisk Canary (Magisk 0646f48e)]

Install Magisk Manager v7.5.1

Open Magisk Manager and navigate to Settings > Update Settings > Update Channel

Select Custom. You will be prompted to enter a custom URL. Use this link to opt for Magisk v20.4.

Press OK.

Go back to the main window and pull down to refresh. It should say

Installed: xx.x [whatever version you had before]

Latest: 20.4 (20400)

Press INSTALL, then INSTALL again. Choose Direct Install (Recommended).

It should download, install and reboot automatically (if it doesn't, reboot manually).

When it turns off, make sure to press and hold Vol+, Bixby and Power until the second time the Samsung Galaxy S10+ logo and the "The phone is not running Samsungs official firmware." message comes up, then let go.

This will make sure the phone starts in "Magisk Mode", as you may be aware already.

After the reboot, open Magisk Manager and verify the installation succeeded. It should now say

Installed: 20.4 (20400)

Latest: 20.4 (20400)

Now tap Downloads from the menu on the left, search and install ViPER4Android FX v2.7.2.1.

Like I said earlier, for me V4A wouldn't install from the flashing process itself, so open the file manager of your choice and navigate to

Internal Storage\ViPER4Android\v4afx.apk

and install the .apk manually.

Open V4A but do NOT install the drivers yet.

Go back to Magisk Manager > Downloads, search and install Audio Modification Library v4.0.

Open V4A again, this time install the drivers. Grant Superuser Access. The drivers will now install. Be ready to press and hold Vol+, Bixby and Power again like before, as the device will automatically reboot without any more prompts or information.

This is where it gets a little tricky because I don't know if it's necessary. From earlier procedures, I learned that you had to go into Magisk Manager and disable Audio Modification Library in order to run the driver install again in V4A, so that's what I did. I encountered problems though, since V4A did not prompt me to install the drivers again, but:

Poweramp did actually process with Legacy Mode disabled, but Spotify and YouTube did not produce any sound at all with Master Limiter enabled.

Enabling Legacy Mode worked for Spotify and YouTube though, so I just re-enabled the Audio Modification Library in Magisk, kept Legacy Mode enabled in V4A and then rebooted my device again.

Since applying these settings and some test-reboots, all apps are processing with both Audio Modification Library and Legacy Mode enabled.

In conclusion, it may have simply worked with enabling Legacy Mode without disabling Audio Modification Library in the first place. Feel free to try it out, and if it doesn't work, you can always just try the cumbersome way I explained in the last step.

Refering to Ms0206's post (#5,116), it may also work with V4A v2.7.1.6 and not having to resort to using Legacy Mode, but for the moment I'm just glad it works for me (and hopefully others) and won't bother with any more testing. If you try this and have different/easier results, feel free to let me know.

Hope this helped!

EDIT:

Okay, one last edit. I decided to go against what I said in the last sentence and just installed v2.7.1.6, because why not. It works just fine, no Legacy Mode and a way better UI.