Hello, thanks WakizashiM. Dropping in some raw info.

Status on sound effect restoration still on hold. Extracted audio files from disc not helped (Hz/pitch/speed problems). So I'm capturing sound effect via emulation, and then "tearing apart" channels to get sound effect.
Sfx's sounded not perfectly in emulator, so they never gonna sound ~same like on ps1. That's leads to not super happy with results VS amount of work needed.

Last progress:
replaced ~464
not replaced ~1677

63 / 123 main
42 / 43 sample00
00 / 50 sample0a
00 / 47 sample0b
00 / 28 sample0c
00 / 50 sample0d
00 / 46 sample0e
00 / 17 sample0f
37 / 39 sample01
45 / 47 sample02
00 / 28 sample2a
00 / 50 sample2b
00 / 52 sample2c
08 / 10 sample2d
34 / 45 sample03
34 / 35 sample04
-- / -- sample05
37 / 39 sample06
44 / 50 sample07
35 / 45 sample08
00 / 45 sample09
00 / 60 sample10
00 / 35 sample11
-- / -- sample12
00 / 03 sample13
00 / 38 sample14
00 / 18 sample20
36 / 39 sample21
05 / 28 sample22
12 / 36 sample23
32 / 53 sample24
00 / 29 sample25
00 / 16 sample26
00 / 19 sample27
00 / 32 sample28
00 / 41 sample29
00 / 82 sample40
00 / 57 sample41
-- / -- sample42
00 / 74 sample43
00 / 76 sample44
00 / 45 sample45
00 / 07 sample46

~95% sound effects replaced until dogs area (right after Psycho Mantis fight).
Some sfx's ok, some of them sounds just a bit weird.

Konami do do do.. sounds (from Psychonauts) while showing Komani logos. Figuring out formats:
pc VOX/vc900021.vox - audio located, BUT not played
ps1 VOX.DAT >01102 - audio located

pc DEMO/ - NO in cutscenes
ps1 DEMO.DAT - NO in cutscenes
So is not cutscenes format.
Codec call file type?!

For PC, maybe is just (and only) textures showed (Konami logos), maybe they even placed in .exe?!
In PS1 is ~10s audio track + ~10s showed Konami logos. Then Cutscene file starts to play.
In PC just showed Konami logos for a ~few seconds (also, is not enough time to play full audio). Then Cutscene file starts to play.

Someone pointed me to this topic, I made a launcher with a pretty comprehensive music patch (not sfx as ReiKaz has been working on) for the game a couple years ago. Speedrunning communities have been using it, but I don't think it's well known outside of speedrunning.

I apparently can't post links, but if you find this video on YouTube by Hau5test:
How to play Metal Gear Solid on PC in 2022 - full tutorial
it has links and a section on using the patcher (at about 7 minutes).

(I say "comprehensive", I mean "as much as it can be with the PC version's music player", there's no miracles like the Evasion fading/slowdown. Also I'm working on an update for it, but no timetable for release.)

Thank you for your amazing launcher and music patch, I hope the remaining audio issues get ironed out in a future release, maybe even integrate Nemesis2000's widescreen patch as an optional feature, though I doubt that will keep speedrunner validity lol.

This should be more known, thus I have added the launcher and music patch in the game's PCGamingWiki page, Thanks!

On my end, the music's in a good place, everything's pretty much how I want it to be given the in-game limitations. All the tracks are mapped correctly and looping nicely AFAIK, and I was able to mod the player to not fade in tracks awkwardly.

There's a very simple tool to encode loop points into otherwise valid wav files at https://mgs.w00ty.com/mgs1/misc/mgsimusicloopadder-a1.zip

Also since I can post links now, my launcher (which has a music pack installer) - https://mgs.w00ty.com/mgs1/launcher

I've briefly looked at SFX, but I feel like ReiKaz probably has the best approach in recording from emu in EternalSPU, as time-consuming as it is. It's totally possible to rip the samples wholesale from the PSX versions, but the game applies some pretty big filtering effects that mean you can't really just swap the files out. The stage-specific SFX sounds completely out of place on PC unless you add reverb manually (and then, how game-accurate is that reverb going to be?), and even the global SFX has some filtering I think.

Edit:
I'm assuming above that Eternal SPU would record the SFX pre-filtered, I'm not too familar with how it works. Otherwise (say, if the reverb was applied to the final mix as a post-processing filter, rather than each channel), I guess you'd be in the same boat as ripping them directly where you have dry versions that you then have to apply your own reverb to.

That said, I recently found out there's impulse responses (WAV files made by analysing filtered audio, that allow you to recreate the filter itself) that you can use with a VST to do a surprisingly good job of recreating PSX reverb, so that's actually pretty feasible.

Still time consuming though :(

There is a cool audio mod on youtube for METAL GEAR SOLID.

EDIT: seems to cover the whole game. It's over 2 hours long. The title is Metal Gear Solid High Quality Audio Mod - PC

I saw it. It is a nice mod. Unfortunately the person who made it is concerned of legal ramifications if he were to publish it, and says he doesn't have the time to show people how to do it. So it shall remain a mystery until somebody else wants to step up to the plate and give it a try.