This would depend on the solubility of the methamphetamine salt. Usually salts of these alkaloids are insoluble in cold acetone/IPA, but there can be exceptions and one would have to look the cases one by one. The first question is to find which salt form meth is most commonly found in (sulphate? hcl?), then search for solubilities of that.
Better look up into TLC and colorimetric reagents to make sure one's mdma does not have meth (or if you're european, see if theres a test center in your country). Also always first try with small amounts, meth has dosages much lower than MDMA. MDMA mixed with meth, depending on ratios, would be way more potent, and the meth (or any other stimulant) will increase the speedy effects of MDMA, as well as possible tachychardia, difficulty of sleeping, and other unwanted side effects.