Please try the UPDATE.

Tried it, made changes for worse

Can't get wifi online anymore after reboot, using USB wifi stick not built in....
Also confirming ceejayemms issue
Seems the whole wlan is centered around onboard wifi alone, disabling the whole thing entirely if not connected in time
Sometimes wlan0 is onboard wifi, sometimes wifi stick gets wlan0 or wlan1
So no bt testing either
Will have to reinstall later this week (time limited)

😔

Update

After reinstall and working around wifi connection, was able to get bt sink working on onboard HP output, no issues
After upgrade to update version
However no audio if I switch my AMP DAC on in system (dtoverlay=i2s-dac) and reboot.
Phone source can connect and stream, but the above device or resource busy messages are back...

Upon start of playback these come by a couple of times:

bluealsa-dbus.py[1873]: rm: cannot remove '/srv/http/data/shm/pidstatuspush': No such file or directory
bluealsa-dbus.py[2238]: mv: cannot stat '/srv/http/data/shm/statusnew': No
such file or directory
bluealsa-dbus.py[3161]: mv: cannot stat '/srv/http/data/shm/statusnew': No
such file or directory

Second and more minor issue : equalizer is not working on bt sink : no mixer defined

3rd not so minor issue
Wifi issues at first boot

Rern
Let us know when to try the update branch for bt audio, I see you're working on it (25 Jan)..
A8