I'm not sure what kind of overhead apparatus you have,but when i use the cone thread i have one of those stands made for that purpose,and it stands behind the machine.If you don't have one of those you can try something like a mason jar or mayonnaise jar(not plastic),and set your cone down inside of that.HTH
Kathi

The thread for sergers(on cones) is twisted the opposite way of regular sewing thread so that sounds like the problem. The tension disc is putting pressure on the thread and it is splitting. Hope this helps. Sewbusy_rn