I am licensed acupuncturist specializing with children in the east bay. and mom's often ask me about soy formula. this does not answer your more specific question but i would like to show you some information about soy formula that many people are not aware of. here are some links outlining the specific dangers of soy for children, especially infants.
Soy formula for infants is outlawed in many European countries and has been shown repeatedly in research to be dangerous to children's health in several capacities. As you will read in some of these articles it has been shown to be a major thyroid disrupter, it disrupts the body's ability to absorb calcium, along with a myriad of other issues.
I bring this up because although your baby does not seem to do well with cows milk there are several options other than soy formula to deal with this. My first recommendation is the amazing homemade formula from the book NOURISHING TRADITIONS by SALLY FALLON & MARY ENIG. It is by far the most digestible and complete formula possible when breast milk is not available. It offers options with Raw cow's milk, goat milk OR a meat based diet. Though it seems overwhelming at first when you first look at the recipe I have several patients who make it and have found that it takes about 20 minutes every other day.
Well I hope this helps and if you have any questions I am happy to answer any that I can.
J. Stevens, L.Ac.