Are SB2 MML and SB3 MML different?

Yes. The syntax is largely the same, but there's a few differences. As far as I know, there's no handy list of everything that changed between PTC and SB3 when it comes to MML. Figuring that out will take a bit of work. You'll have to compare documentation for both versions (the PTC manual is here), and probably do some experimentation on top of that since the docs don't always cover everything (e.g. multiple dots).