In my experience, box-shaped rooms, even if they're cube-ish, are the easiest to treat acoustically. Rooms with extra corners are a pain acoustically, and require a lot of extra acoustical treatment. Speaking of corners, that's a good place to start. Corners generally act as distorted sound sources (think megaphones), so if you can control the sound in the corners, you'll go a long way acoustically. If you take a look at the RoomTunes product pages on the MusicDirect website, you'll see in the illustrations the typical corner locations that should be treated. Further, you can educate yourself in a hurry just by putting on some music and holding pillows, sweatshirts--most anything acoustically absorbent--in the corners and along the walls, and listening to the effect. Then you'll know where you most need treatments. Even without all the acoustical theory, you can become an expert on your own room.
As for me, I've been successful in multiple rooms with GIK (the highest WAF, btw), RoomTunes, TubeTraps, and some other treatments. Different products and approaches, BTW. All have worked. Placement has consistently been an important factor. All that said, seems to me that you are on the right track.