Edit: Almost forgot,
@RivalK93 I'm using your 'cancel' sound (if that's cool)
Sure, it's cool!
I'll give it a week or so for bug reports, if no issues are found I'll do a pull request after that.
• Animation-playback timing is perfect, no sound skips. (Except for when pressing rename and back multiple times really fast (because of long message sound effect), but WHY would anyone do this??

Plus it does not break anything or feels off. So i guess it is not important. I think I would leave it as it is too.)
• I noticed that in your builds made from the sfx-merge branch when i select "Start HDL Server" from the Menu (using a PS2 slim, so it should not start), the whole application freezes at "HDL Server Starting..." without printing a "Failed to start HDL Server" message when it fails. And you have to restart the console from there on. And I have not the slightest idea why this would happen because i do not own an original network adapter for my fat consoles and i have not used this feature. So if anyone uses it please make a test.
• Next is that when OPL (ifcaro, ps2-home DB) is initializing, showing only OPL's splash screen and loading icon, the user is able to explore the Menu options even though it is not being displayed. And enter the options, e.g. "Settings", "Display settings", which are then displayed over the splash screen and if they are still on display by the time OPL is ready to fade out the splash screen, it causes OPL to freeze. Note that the buttons used to explore the Menu screen are D-pad Up and Down, Cross, Circle ans Start. In your sfx-merge builds if you press any of those buttons during initialization it causes OPL to instantly freeze (without even displaying anything more). I think it is caused because it should play a sound if you press any of these buttons and OPL is not ready to. So it freezes. It is not happening with any other build i found, ifcaro, ps2-home DB, or even your gui final build. So that is my guess. IMO the user should not have the option to press any buttons until OPL is ready to fade out the splash screen. So if input was (somehow) to be disabled until that time this should fix the issues in all of these builds.
Boot up sound isn't amazing but the idea was to keep it simple, this doesn't even have to be the one that gets compiled in if anyone is able to provide a better & suitable royalty free one...but its taking a long time to try find/make one so this is it for now.
I agree, boot sound is not amazing. I have found an other option which i tested and i really like! And i can also explain why. It is simple, has nice stereo sound, it is still short, creative commons licensed, not genre specific and it has the epicness i need when i boot such a kick-ass homebrew project! I cannot post the link here, the site will not let me, but "WelcomeToWhatever" from eardeer on freesound org is the sound. But it is not the one i used to test how it sounds. I choped up the dead waveform and made (mainly) the first half shorter in duration. It starts playing when the splash screen fade out starts and happens to "burst" exactly(!) the moment splashscreen is completely out. It is just perfect. This guy has done an amazing job.

According to the cc licence i am free to share and adapt this sound, so here is the one i finally used and propose: