I have no experience with Musescore, so I can't comment meaningfully myself on what might be possible within that, but for using Hauptwerk's built-in MIDI player to play MIDI files created by software other than Hauptwerk, have a look at these topics:
viewtopic.php?f=4&t=19852&p=148963
viewtopic.php?f=19&t=18810&p=141645#p141637
mdyde wrote:Hauptwerk's built-in MIDI recorder/player uses and requires the MIDI implementation described in brief in the 'Recording and playing back live solo performances: the built-in MIDI recorder/player and its fixed, predefined MIDI implementation' sub-section of the Hauptwerk user guide (page 236 in the current v6.0.2 version), with the full implementation documented via the 'Recording | View Hauptwerk MIDI recorder/player fixed, predefined MIDI implementation (for this organ)' menu function within Hauptwerk (with the relevant organ loaded).
Hence if you want to play a MIDI file using Hauptwerk's built-in player you need to make sure that your MIDI file uses that specific MIDI implementation, editing the MIDI file externally to Hauptwerk accordingly if needed.
mdyde wrote:Alternatively, if you wanted to interface [your MIDI editing software] directly to Hauptwerk (rather than using Hauptwerk's built-in MIDI player), see the 'Composing pieces off-line from MIDI notation software' section in the guide [pages 248-252 in the current v6.0.2 version].
mdyde wrote:(P.S. We do also have an enhancement request logged regarding potentially adding the ability for Hauptwerk to import MIDI files that had been saved from other applications, with Hauptwerk applying user-defined MIDI implementation mappings as it opens/imports them.)