Everything is relative. Cabling thicker than my arm or my **** (bad fred, bad fred ) will be a waste of money. Cabling thinner than spaghetti will be a waste of technology.
__________________
"Don't disturb my circles." translation of Archimedes last words
Improper Language/Behavior: Part of this post was modified because it did not adhere to the behavioral policies of this site. Please review the CR4 site policies and FAQ.
There is a term PMPO which is Peak Music Power Out Put, it is used by the manufacturers to bluff the customers.
While the 6000 W in your case is PMPO you do not have to worry about the cable size, the nominal sized cable provided by the manufacturer with the equipment will work satisfactorily.
__________________
Knowledge sharing is a WIN-WIN situation