@Blake00 It's been awhile since I worked on sounds for Medieval Millennium, and even then I admit I didn't dig too deeply. As others have said, in ToT you can't
specify more than one custom sound per unit (I never even realized that the MGE unit editor let you do that!). But units can still
play more than one sound, especially for events other than combat. I'm not too familiar with how the "fallback" sounds work if you specify a sound of
<none>, so I can't really comment on that, but even if you
do provide a unit with a specific named sound file in @ SOUNDS, additional sound files will still play as well in some cases.
For example, I had to override
Jetcrash.wav and
Jetsputr.wav with tiny silent files because those sounds (from the Original/Sound folder) were sometimes playing, even though I hadn't assigned them to any units and every unit had its own sound file specified. There are other files like this as well, that I didn't override because they worked for my scenario -- for example the one that plays when a Trireme sinks (I believe this is
Boatsink.wav in the Sound folder directly beneath the main game installation folder, rather than the folder within Original).
Unlike MGE, where sounds were apparently slot-dependent, I think in TOT these extra sounds are purely dependent on the properties of the unit type -- as I recollect, any domain 2 unit with the "trireme" flag will play
Boatsink.wav if it's lost due to ending its turn away from shore, regardless of the unit slot it occupies. (In MM, my ships with the Trireme flag have IDs 82 and higher, vs. 32 for Trireme in the base game). Pretty sure the same is true for the Jet sounds, and maybe other things as well, although I've never seen or developed a comprehensive list.
So my conclusion is that if you're able to avoid
<none> and provide actual sound files for every unit, then "fallback" sounds wouldn't matter and you don't have to worry about slot assignments. If I'm understanding the capabilities of the MGE unit editor correctly, then I guess the main changes in TOT would be: (1) the sound filenames for these other events are hardcoded into the game itself, so any custom versions you provide have to use the existing names; and (2) all units with a given set of properties will trigger the
same file(s), so you can't customize them uniquely per unit.
Hope this is helpful, and good luck with your project!