If it's me, I would focus on the aro. If I'm able to upgrade for my clown trigger, my 200 might house a solo jardini (similar size and temperament to your asian) one day.
From what I understand, an Asian aro is a grail fish, much like the clown trigger is for me. Proper attention and care for your aro in a proper tank will yield best results and the most impressive fish. Getting distracted with crowding the tank and adding a large competing cohabitant like a gar may not be in your aros best interests.
This is all coming from a guy who's never kept rays or aros though so best of luck with whatever your plans may bring.