I don’t understand your problem. The 3.5mm output is SE, and the 2.5mm output is balanced. A single ended cable goes in the one, and a balanced cable goes in the other - and not at the same time! The M9 doesn’t ‘switch’ between SE and balanced - you do, buy using the appropriate cable. So if your balanced cable is damaged, use a SE cable with your IEMs or headphones and plug them into the SE output (3.5mm).