Bluetooth headphones will not work with certain programs

I use Linux Mint 20 and have successfully installed JACK which thanks to Cadence works well in conjuction with PulseAudio.
Subsequently I was so pleased with myself when I manged how to get my bluetooth headphones working thanks to posts on this forum.
I tend to use the CLI programs 'alsamixer' and 'pulsemixer' to control all my volume needs.
So my bluetooth headphones ( yes I have 3 different brands - all work ) well with Audacity, Celluliod, Zoom, - all the 'usual' audio visual programs BUT ....OH NO ....DISASTER.... I can't get them to work with:-

• Frescobaldi ( front end for Lilypond)
• Rosgarden ( My favourite DAW)

both of which rely on MIDI sounds provided by QSynth
Oh yes these programs work well through the laptop speakers or WIRED headphones but not bluetooth.
Could anyone point me in the correct direction?