I have quite a bit of experience w/ this and I will tell you that Ensure mixed w/ milk and slightly frozen makes a good shake. I also like mashed potatoes made thin w/ milk and chicken or beef base. Protein powders usually have a weird taste, but I have been using something called Beneprotein. You can mix it with any soft/liquid food and it's undetctable. If his energy is low it could be that he's not getting enough calories. I also take Benecalorie. Again, undetectable. And for the times when I just want something really delicious, I mix up a thin cake mix, chill it, and drink it with a straw. I know that you want to check all this w/ his doc, don't know if he needs extra protein or calories like I do. If you need more suggestions, you can pm me, I'm full of 'em. Good luck to you both.
Be the kind of woman, that when your feet hit the floor each morning, the devil says "oh crap, she's up".