Hi Zymie,
Thanks for the question - we've kept the Burton Water Salts out of the water calculator to date due to it's unpredictable combination of ingredients. Since it's a blend of a few different things and it's hard to identify exactly what ratios of salts go into each, it's difficult to make the exact predictions in the calculator. There's a discussion of this over on HomeBrewTalk here: http://www.homebrewtalk.com/showthread.php?t=93695
Your best bet might be to try using some of the suggestions as to the composition in that thread to enter the components into the calculator. Hope that helps!