as well depending on which was ingested first they are both broken down into their metabolites by the same enzyme so it would differ in effect that the enzyme will be busy breaking down the tramadol alowing for a higher bio availability of the mxe with metabolite o-desmethyl tramadol and the opposite will result in the concentration of the mxe metabolite ( dont know exactly) and the un metabolized tramadol
edit ps. the o-desmethyl would probably cause the most synergistic effects