Mac OS 11.7.8 16GB memory, Sibelius Ultimate 2023.6.  I imported a MusicXML file from Dorico 5.  It plays back fine, except for unpitched percussion instruments, which don't play back at all.  I did not let Sibelius choose the instruments.  When I edit the instruments, the percussion instruments have been added to the family as (for example) "Bass Drum MusicXML."  For these instruments, no "editing staff type" produces any sound.  For the same MusicXML file, using Sibelius 7 Sounds instead works beautifully.  I prefer using GPO5, since I can use the resulting MIDI file outside of Sibelius.  Incidentally, using GPO4 instead of GPO5 shows the same problem