holsen
Headphoneus Supremus
Several pages back, there was a good discussion about this. The consensus is that the M3X at most "runs slightly warm" with extended play in Balanced. My M5s got quite warm in balanced and got quite hot when playing in balanced with the charging cable plugged in. It's a non issue on the M3X.A better question is if it gets hot when running in balanced for hours while in the official leather case. Because you know that a case traps the heat that would otherwise easily be transferred out from the interior.
I know for example that a FIIO M15 I have runs hot if playing for a while, and that's even outside the case. I worry so much about those little components that I even have a $20 Polar handheld fan blowing at it (very quiet) if I plan to use it at home for extended periods.