We already have a workaround with the 'force single in/out usb dev' which is accessible via preset 10 or can be set in the rk006/settings page / app:
We can't change the hardware fact that there are 3 midi buses for input and 11 buses for output. Sorry to say the solution is with OSX, not with us. If you force the RK006 into single I/O bus You might need to clear out device cache on osx to make the system actually show only 1 port in and 1 port out. Set the RK006 to single I/O, save to boot and unplug it. Delete the existing greyed out RK006 entry in your OSX 'audio midi setup' then plug it again, the RK006 will appear with only 2 ports.
But I must add: As I look at my crippled OSX system now: Sending to OUT_ALL still access all outputs on the RK006 and there are 7 individual outputs left. There must be some very rigid MIDI devices with multi-midi channel response in your setup if this Apple fkp cripples your system:
Individual port 1-7 can send out to ANY of the 16 MIDI channels without hindering gear on other ports? So put the devices which ask a lot of channels of any of these ports.
Then connect the devices with simpler MIDI channel response on hardware port 8-10 and set them to different MIDI channels. Set a filter on the RK006 which blocks (at least) these channels to output 1-7 so midi to out_all will not be sent to these ports. Here an example which filters out MIDI channels 1,2,3,4,5,7,8,10,11 and 13 to port 1-7
And this is the worst-case scenario: If you have devices which just have 'normal' single MIDI channel response you will have no problems if you can just set every MIDI devices to a separate MIDI channel and access all of them via OUT_ALL without interfering with each other. The workaround is there but Sonoma needs to be fixed.