You have a number of export options. Likewise, there are a number of import options. It depends on what's on the receiving end.

Who's receiving? Users of other apps? Older versions of Finale? Give us a clue — the answers are dependent on knowing these.

In short, MusicXML is a set of tools that developers incorporate into their apps. What features are included, how and how well are up to those developers. In addition, there have been many version developments over the years.

How are your fingerings done? Are they attached to notes in some way, or are they text blocks? I would think your chances would be better if they're created as articulations.

I tried multiple export options (from 3.1 all the way down to 1.0, compressed and uncompressed insofar as it was allowed). Nothing seemed to change. The files are being uploaded to Soundslice. I have asked the client if there are specific settings required by Soundslice and have yet to hear back on that issue.

The fingerings were entered as articulations. 

You appear to be at the mercy of the Soundslice developer and how he/she implemented MusicXML. Knowing the build of MusicXML will help but won’t tell you what features were implemented and how. Unfortunately, it’s not something that one just drops into an app and, Voila! everything works as expected.

See if Soundslice will tell you what works (apps and version export) so you’ll have a clue.

A few examples: A composer I work with uses Sibelius but likes my extensive VI library to realize his scores. I get the .xml files but they don’t play as well with Finale as I’d like—can be done but takes a lot of time. Notion 6, however, opens them perfectly and lets me assign my VIs and the mixer makes it very easy to get the mix he wants. The $79 crossgrade to N6 is worth every cent for the time saved.

Encore uses Mxml 1.3 (Mac) 1.1 (Win). It cannot import/export lyrics or expressions. Someone posts on a lot of forums that it should because 1.x supports this. I neither know nor care because the app doesn’t support this functionality. It doesn’t matter that the toolkit does. 

The fanboys on the Dorico forums keep touting the improvements if its handling of MusicXML. It’s their knee jerk reaction every time someone complains. The fact is that it’s not as good as it should be as Mr. Spreadbury readily admits. Finale, Sibelius and Notion handle it better. Hopefully, that will change soon.

Good luck with this.

Some Dorico users find that feeding XML files through Finale or Musescore helps prep the files for Dorico import. The truth is that not everyone supports the full implementation of XML in their notation programs (shades of early HTML), and that's just the way it is.