It is subjective, your friends may not have died from combining DXM with MDMA...im sure there are plenty of people who have done both at the same time and lived to tell about it but the truth is the combination puts you at high risk for serotonin syndrome, which isnt a cool way to die.

http://drugs.greenparty.org.uk/substance/dxm.htm
http://www.maps.org/news-letters/v09n4/09447sfe.html