There seems to be considerable personal variation with regard to palatability of casein hydrolysate (and also, incidentally, BCAA’s.)
Personally, I have no problem drinking MAG-10 unflavored, but that’s clearly not the case for everyone.
I did some experiments a couple of years back with regard to improving taste of BCAA’s, after learning of a rather exotic taste-masker (it didn’t work in this application, by the way.) What I found then was that the most important factor was the simplest one: with enough sweetness, the palate accepts the taste of the amino acids. I never found any very substantial improvement beyond that obvious one. The Biotest liquid flavorings have succeeded in going well past that, though.
However, simple sweetness remains rather effective even if by itself.
Just for fun, and since it may be useful information for you, I’ll try some xylitol (1 tbsp) and MAG-10 right now:
Ah, well actually it did about nothing. It tasted nearly the same as unflavored MAG-10.
Increasing to 2 tbsp did provide some noticeable sweetness, but the taste was very predominantly still that of CH.
It seemed unreasonable to me to go past 2 tbsp.
So I’d have to say that xylitol does not work well for this application.