Have you modelled your room in Cara yet? I would suggest modelling it with the cabinets filled with faced cotton and without, and see which is better. My initial guesstimate would be that the room would probably perform well if they were turned into bass traps, but make sure they're absorbing bass only. If you turn them into broadband absorbers you're likely to mess up the imaging due to their asymmetrical placement. They might even be good candidates for tuned absorbers.