It seems that a simple approach would be simple linear regression of Y on X using the Bivariate platform. If you establish a high correlation, then Y is essentially redundant. This analysis does not determine if X or Y is the response. Either one could be the response. So the decision, without additional information, is arbitrary.
A more complex approach would be partial least squares of (X,Y,Z) on (A,B,C,D,E). PLS can tell you about the correlation among the factors, among the predictors, and between the factors and the predictors. PLS can indicate if X and Y are correlated and if they are related to the factors the same way.