Multipart Capella: Mixer only shows one part

After I import files from Capella into musescore I would like to be able to see more than one instrument in the Mixer.
For example, I import a file consisting of S, A, T, B, and piano. In musescore this is displayed correctly on six staves (two for piano). However, in the mixer I only see one instrument/part.
Is there a way to separate the staves into separate instruments?

If I export from Capella to MusicXML and then read into musescore, the mixer does correctly see several parts. It would be more convenient to read the *.cap files directly, and in one case I couldn't use this route because musescore crashes when reading the *.xml file.

Any help would be greatly appreciated!