Oh this is a bit more tricky, but I know all about this so allright, let's get started shall we?
1. "Play wav" trigger is only for script-related short sound effects, like alarms, a vertibird coming at that exact moment, etc. You can even localize them on a entity.
It is also heavy in file size (.wav instead of .mp3 for soundscapes), and it requires a sound ID which means that it can create problems if you use the same ID twice I imagine, like playing only the second scripted sound probably. So, I am quite sure you will not need that.
2. Sound file is a little bit more cryptic, but very customizable so it is great in fact. It is the core of the soundscape in Tactics. You don't import sound files using "Import sounds file" option bhahahha (This is true!), instead you import a code text file (.txt) that contains lists of .MP3s, their location within the map (sound zones), volume, etc. etc. etc. It looks like this :
Code:
ambientSoundTable =
{
ambiant, //THE NAME OF THE SOUND ZONES
}
//FILES
ambiant_numOfFiles = {1} //How many sound files in "ambiant" sound zone
ambiant_random = {false} //Play files in random order true or false
ambiant_file_0 = {sound/custom/AutorouteDetruite.mp3} //File path of course
ambiant_volume = {100} //Default volume for ambient sound zone
//TIME OF THE DAY
ambiant_timeOfDay = {always} //When this sound plays: day, dawn, dusk, night
ambiant_notTimeOfDay = {false} //So you can do NOT night and it will play all other times
//PLACEMENT
ambiant_zone = {Ambiant} //Limitation to a particuler zone
ambiant_overrideZone = {} //Don't play this sound if in this zone, multiple zones are seperated by ';'
ambiant_useRadius = {false} //this ambient has a position and radius
ambiant_position = {Integer3(0,0,0)} //where in the map the ambient is - you can get the position for the sound in the level editor by holding the mouse over a tile and looking at the tiles bounding box.
ambiant_minDist = {0} //Distance before volume starts to fall off
ambiant_maxDist = {15} //Distance from ambient that sound cuts off
//LOOP
ambiant_looping = {true} //If not looping we use minTime and maxTime
ambiant_minTime = {20} //MinTime between non looping sounds (secs)
ambiant_maxTime = {120} //MaxTime between non looping sounds (secs)
//VARIATION
ambiant_volumeVar = {0.0} //Variation in volume 0.2 = 20% variation
ambiant_pitchVar = {0.0} //Variation in pitch 0.2 = 20% variation
How to add an sound zone :
First you need to go to the map where you want soundscapes and create a sound zone. You enter Map editor, click on the Zone tab, Click "add", go to the bottom level you want to place your sound zone (meaning the lowest place the feet of the characters will walk for the zone to play the sound), using mouse wheel to go down to the desired level. You ckeck Bottom and you click on the map at a desired place. You will see your cube will change shape. You then do the same with Top and you have your soundZone localized. YOU THEN HAVE TO CHECK "SoundZone" in the bottom, imperative.
Here you go! If you :
1. Customized a sounds file using my code and added it to the map using "Import sounds zone" option.
2. Created sound zones that match the sounds file.
It will work I am sure of it.
NOTE : Changing the file will not update the soundscape. Sad to say, but you will have to go back to that map, reimport the sounds file, and only then it will be updated. This means the sounds file is integrated to the .mis file.
IMPORTANT : These soundscapes are permanent and always on, meaning that I don't know of any way to script them, make them stop, except by programming them for specific times of the day or location. If for example you setup an alarm as soundscape, there will never be a way for you to turn it off. So just use the Sounds file to program soundscapes that are permanent. Use the script "Play Wav" for all other sounds that could be turned on and off.
I also tried the "play wav" trigger but it only played a very small part of the actual wav file as a loop and I didn't find that useful. The "import sound file" thing was also weird to me, as when I tried to export a sound file from another map I couldn't find a good way to edit it to use on my own map.
I tried both ways but neither one did the trick yet. I'm sure I'll get it to work eventually though, thank you so much for all the help! 
