Here are the files from iaspkg0.exe. I extracted them using Resource Hacker.

Well that totally works too. Thanks so much for your work!
Unfortunately, I wasn't yet able to get the surround sound in my test game to work properly (it's Boss Rally). However, I think I'm moving somewhere.

First, I tried working through the IAS control panel applet. If there's no earias.dll, only earpds.dll - it will report the following:

1earpds.dll -- 
2	found in C:\Windows\system32\earpds.dll
3	target = 1096
4Microsoft DirectSound, DirectX 5, DirectX 6
5	version 1.58
6	target expected: dsound.dll 5.00.1871.1
7	target found: version 10.0.22621.1
8WARNING -- earpds.dll targets an older version of DirectSound; check www.earsound.com for upgrade of earpds.dll
9
10	functioning properly
11
12earias.dll -- 
13	no multi-speaker IAS component installed;
14	program detects drivers on your system supporting
15
16	Aureal A3D
17
18	Visit www.earsound.com and download
19	the IAS component for this sound card.

The part about A3D is because of Creative's Soundblaster Titanium HD drivers (and many other versions to my knowledge) which drop a rudimentary a3d.dll wrapper.

Next with the Aureal A3D earias.dll version in SysWOW64 folder:

1earias.dll -- 
2	found in C:\Windows\system32\earias.dll
3	target = 1048
4Aureal A3D Vortex
5	version 1.58
6
7WARNING -- your card is using an uncertified A3D.dll; this component only works with Aureal-Certified hardware.
8
9	component fails.

(I truncated the part about earpds)

So it doesn't know this A3D.dll and bails out. The speaker settings (where the surround panning is being tested and the earpds.dll can be disabled) part of the applet tells that earias.dll failed during initialization.

Next, the SB Live! earias.dll. That would be the preferable one as it allows the use of EAX sound effects:

1earias.dll -- 
2	found in C:\Windows\system32\earias.dll
3	target = 1072
4Creative Labs SoundBlaster Live!
5	version 1.58
6	target expected: sblfx.dll 4.06.615

Even though it doesn't report "the component fails", I think it's not loaded. The speaker setup says the same as with A3D. I'm not sure what is sblfx.dll it's looking for. I believe it's some old school way to read the speaker configuration. Likewise, I tried putting some random sblfx.dll into SysWOW64. The component fails too, however now I'm getting Ear Error:7: GetConfiguration failed in the sound card software. Need to try different sblfx.dll versions.

Next, the Diamond MonsterSound earias.dll:

1earias.dll -- 
2	found in C:\Windows\system32\earias.dll
3	target = 1024
4Diamond MonsterSound Original
5	version 1.58
6	target expected: f3api32.dll 4.10.00.1582

I don't know what API it is looking for. A quick googling tells me that f3api32.dll was distributed with MX300. The MX300 is an A3D card. So I'm not exactly sure what's going on here, but the component fails nonetheless.

Next, the SB PCI-64/128 version of earias.dll:

1earias.dll -- 
2	found in C:\Windows\system32\earias.dll
3	target = 1060
4Creative Labs SoundBlaster PCI-64, PCI-128
5	version 1.58
6	target expected: eapci.vxd 4.05.1207

eapci.vxd not found. Definitely some stuff for system configuration reading. Yet, it seems that the dll gets loaded properly and surprisingly the speaker config is working. You can test the audio output and the rear/center speakers do work. Which I'm not sure why because I don't have system-wide dsound redirect. Somehow it manages to output surround audio here.

So that's a start. However, Boss Rally still outputs in stereo only. What's interesting is that you can remove all the dlls from the SysWOW64 folder, rename earias.dll to earpds.dll and run the game. It will initialize fine (with all the other earias.dll it won't load and complain about either audio hardware not initialized or that the system is set to output stereo only, so use earpds.dll). No surround sound, though. It might be that this game has no surround sound at all.

I'll try to find other games which explicitly support surround sound and have some settings for that - and report back.

Edit: I think now this thread is totally unrelated to Marvin, so may I please ask moving it to The Guide\Windows?

Yay. It works! I found another game that uses IAS middleware - it's Heavy Gear 2. And it does work in full surround!

So with earias.dll of Creative Labs SB PCI-64/128 variety you get surround sound without any additional settings in-game. However, you must make sure that the "I always want to use "Phantom IAS" solution" on the Speaker Setup tab is unchecked (see the screenshot).

Also, what's still a mystery to me is that how the hell does this work. It outputs with proper 3d panning without any dsound.dll redirects on my Windows 11 system. No OpenAL redirects, no nothing. Such a weird thing.