This is not what I am asking.
This is what I am asking: Can I play my midi controller while playing back a progression in iReal Pro.
While listening to the progression in iReal Pro can I play along with a midi keyboard?
Are you asking if there's a way to use the your MAC to both play/display iReal pro and at the same time, accept midi data from your controller to play (midi) notes/sounds as well as the iRp track?
Are you asking if there's a way to use the your MAC to both play/display iReal pro and at the same time, accept midi data from your controller to play (midi) notes/sounds as well as the iRp track?
iReal Pro does not accept midi input from outside itself, so you would have to use a sampler app (or similar) which would be played using your midi controller.
I tested a midi keyboard connected to my audio interface (with midi input) connected to my MacBook Pro. I was able to trigger sounds in Apple MainStage (v3) while a track in iReal Pro was playing. Audio from both was heard using headphones connected to the MacBook Pro.
Even though you are running an old OS, presumably you should be able to do something similar with your setup and a sampler app.