PCA can certainly give some insights in your problem. Run PCA in your data and look at the different principal components. In you case, I guess the four variables would dominate in one principal component (presumably first) representing characteristics of A and the rest two variables would dominate another principal component (presumably second) representing characteristics of B. To make it more clear, when you look at the coefficients of the first principal component,the first four values should have higher values than the rest two. Similarly, in the second principal component, the last two coefficients should have higher values than the first four. Of course, I am presuming that A and B are distinguishable.