Anne, Have you tried the Carnation 560? Dave didn't like the Ensure stuff and I don't think he would be the PR person for Carnation but he does tolerate it pretty well.
We couldn't find it locally but were able to order it online.

He also (through someone's recommendation here) is using Juveun(sp?) and that seems to sooth his mouth before he tries to eat.

This is from the sore he has BEFORE treatment so I can't even imagine what it will be like at the stage you are at!!!