I think high intensity circuit training is a good way to go to improve fight conditioning mixing resistance exercises with cardio. Working for 5-6 minute rounds is a good idea when training for an MMA fight. Some ideas below that may help. Do 30 seconds per exercise and repeat twice through for a 5 minute round with 1 minutes rest between rounds.
Ground and pound
Dumbbell push press
Hanging leg raises
Dumbbell snatch 30 seconds per arm
Medicine ball russian twists