What happens if i overpower my 6x9 car speakers?

so i have a bit of an issue, i have 2 12 inch subs, and 2 6x9 speakers. my amp is 2000 watts and its a mono. it requires 4 gauge wiring to operate, this amp powers my subs. i have a seperate 400 watt amp powering my 6x9s. heres my problem, i have 4 gauge wire going to my distribution block. then from the distribution block, i have 10 gauge going to the 400 watt amp, and 4 gauge going to the 2000 watt amp. i realized that the 4 gauge wire isnt really 4 gauges if its powering 2 seperate amps. i took it out of the block and put it in the amp and the subs hit way harder. i was thinking of wiring the 2000 watt amp to the speakers but i know overpowering can ruin subs and speakers. what should i do!