I wish I had the magic answer. My husband said only sweets tasted okay and got full very quickly also. It turned out that he had an obstruction at the beginning of his stomach that wasn't found until right before we were released to hospice care so ask the doctor if there is any obstructions in your husband's gi tract.
If he'll eat sweets, put fiber and protein powder in every thing he'll try. Also try the Ensure Plus since it has more calories. If all else fails, ask for a feeding tube. My husband wasn't a candidate for that, but there were many people who had a feeding tube for a while at his clinic and many had lost forty pounds before it was put in and they gained most of their weight back, and did not use it after their appetite returned.
Best wishes for a fast recovery