Sound may be quiet in game. Try turning up the gain in audacity. If that isnt it, it isnt defined properly in the csv. Glad to see you working on the EE +1

[...]
triggers[i] thread detect_song_activation();
[...]

--------------

detect_song_activation()
{
	self playsound("ee_song_loop");       //    <<<<<----------- here
	while(1)
	{
		self waittill("trigger", player);
		self trigger_off();
		self StopLoopSound();
 
		playsoundatposition ("ee_song_activate", self.origin);       //    <<<<<----------- here
 
		level.trig_mus_count++;
 
		if(level.trig_mus_count == 3)
		{
			thread play_ee_song();
			player waittill("song_done");

			self delete();
			break;
		}
		wait 0.1;
	}
}

Did you try adding a print before self delete(); and make sure it is waiting and not deleting the trigger, killing the sound?

Edit, doesn't trigger_off just move the trigger 10000 units down, like hide? Thus playing the sound, but 10000 units below where you think?

I commented out the trigger_off(); and still no sound.

trigger_off( name, type )
{
	if ( isdefined ( name ) && isdefined( type ) )
	{
		ents = getentarray( name, type );
		array_thread( ents, ::trigger_off_proc );
	}
	else
		self trigger_off_proc();	
}
 
trigger_off_proc()
{
	if ( !isDefined( self.realOrigin ) )
		self.realOrigin = self.origin;

	if ( self.origin == self.realorigin )
		self.origin += ( 0, 0, -10000 );
	self.trigger_off = true;
}

disable_trigger()
{
	if( !IsDefined( self.disabled ) || !self.disabled )
	{
		self.disabled = true; 
		self.origin = self.origin -( 0, 0, 10000 ); 
	}
}

Yes it does move it down, just checked utility.gsc . That has got to be the problem make it look like this:

[...]
triggers[i] thread detect_song_activation();
[...]

--------------

detect_song_activation()
{
	self playsound("ee_song_loop");       //    <<<<<----------- here
	while(1)
	{
		self waittill("trigger", player);
		self StopLoopSound();
 
		self playsound ("ee_song_activate");       //    <<<<<----------- here
		self trigger_off(); // You should probably just delete the trigger here. Why just turn off?
 
		level.trig_mus_count++;
 
		if(level.trig_mus_count == 3)
		{
			thread play_ee_song();
			player waittill("song_done");

			self delete();
			break;
		}
		wait 0.1;
	}
}

I removed the self trigger_off(); for testing purpose, and tried both "playsoundatposition" and "playsound". Sadly none on them works.

detect_song_activation()
{
	self playsound("ee_song_loop");       //    <<<<<----------- here
	self waittill("trigger", player);
	//self StopLoopSound();

	self playsound ("ee_song_activate");       //    <<<<<----------- here
 
	level.trig_mus_count++;
 
	if(level.trig_mus_count == 3)
	{
		thread play_ee_song();//is this meant to be thread on level or self?
		//player waittill("song_done");
 
 
	}
	wait(3);//testing timer
	self delete();
}

Don't play sounds on triggers

It causes a random model to appear

Had this issue myself and took me forever to find out that was the cause

Playsoundatpposition

Or spawn a script origin or something "at" the trigger and use that

I had a random pair of zombie legs appearing in front of my pap for weeks coz of this