Back in the day…..
I ran the head unit into an EQ that had front and rear level adjustments. The EQ also had a sub output. The EQ ether had a selectable cross over point or a sliding scale lever.
Today, you can find a powerful amp to power all 5 speakers.
Back when I was doing this, it was an amp for each section.
Front, rear, sub.
Take a stroll through Crutchfeild on line to see some of what’s available for amps. The one suggestion I can give is when it comes to an amp, the less distortion the better, more power the merry even if you don’t turn it up all the way. It’s just cleaner power filling the speakers instead of struggling to get there.