Diffusion or Absorption

I'm completing the construction of my home media room (and home theater). Would like some thoughts on dealing with the solid core steel doors. I have a single door midway back on the right hand side, entrance from the rest of the house. And, I have a double solid core steel door in the back left of the room, outside entrance and exit. I originally was going to treat them for absorption, but now I'm thinking perhaps diffusion is the way to go.

Few other pertinent facts. Room measures 14 x 24 with 9 foot ceilings. The walls are double sheetrock with Green-glue hung on metal hat channel. I have GIK acoustic bass traps and diffusers in the back corners. In the front corners I have basic foam absorption and a heavy drape that covers the entire wall....Thanks
Congratulations on a really nice size listening room. GIK has quite a few wonderful products and I've found them to be a great deal of help. Acoustic Fields with Dennis Foley has a wonderful product regarding  truly effective low frequency absorption. I suggest you contact him. 
From the description it sounds ( no pun ) like the room is well set up!
Diffusion will decrease energy.
Set up the playback system and work on room modes.
Then you will have a better idea of placement and type of treatment.
From other conversations I have had, and testing for myself, I would recommend you remove the foam in your room and replace it if necessary with GIK panels. The steel doors? How about self-adhesive carpet tiles?
Analyses the effect of the doors to your listening area using a mirror. They may have minuscule impact. 
Thanks all for the great suggestions.... I've actually ordered some great looking acoustic panels from Acoustimac to place on the doors. Since the doors are steel I'm going to use neodymium magnets to anchor them to the doors.