Hey. I'm looking at some amp heads and cabs and since I'm pretty new to this (I have been using combos) I am slightly confused about the power ratings. I have figured out the Impedance issues and I have some questions about power. Let say the head is rated at 600w@4ohm (TraceElliot AH600). Do I have to use a cab rated at 600w or can I use, let's say a 400W or 800W (all @4ohm)?