Alright, I bothered to look into it right now and here's something strange. The game DOES NOT load the title screen music from the AST file in the Stream directory. It's actually found in one of the AW files, but we can't edit this stuff right now. So the title screen music file in the Stream directory is actually an unused duplicate.
I don't believe this. Remember when Mario posted all the sequenced soundtracks as midi in the Discord group? I was hearing through all of them, even noticed that the Fire Flower, Ice Flower and Red Star themes are dublicated, but there was no midi sounding like the title theme. Although, the File Select Beat was in the midis.
Sierra, your're really making us break our heads xD
Why don't you try replacing another soundtrack to convince yourself how AST-replacing works?
I checked your AST. It's properly set up, you've done a good job. But seemingly the title screen music is one of the sequenced soundtracks. Sequenced soundtracks are pretty complicated to figure out. As said before, the Fire Flower, Ice Flower and Red Star themes are sequenced soundtracks for example. I am sorry Sierra. Still, try replacing any other AST-file which isn't listed as "unused" in my tutorial, that shall work!