Plan9: I don't think he said he's afraid of losing muscle, but that he is afraid of gaining fat, which would make his muscles look less defined.
That said.. you don't really need to drink those weight gainers. Regular protein shakes can have a lot of calories as it is. Do some searching on
www.bodybuilding.com They have an excellent protein database (then search elsewhere for lower prices.. it's cheaper half the time). Find something that you think would fit your needs.
Oh, and I do not recommend ProM3 by ISS. It tastes like crap and mixes poorly. Pro Complex by Optimum Nutrition tastes really good mixed with soy milk (but not so good with water).