Ok...i have a Marshall MG100 halfstack combo. But i wanna upgrade my head to an AVT150 head. I need to know if its possible to use the AVT150 head with my one MG412 cab. Would the head be too powerful for the speakers? I really dont feel like buying a 1960A cab to use the AVT150 head, but if that what it takes...

It will work without a problem. The cab rated at 400 watts and the head at 50 watts!