Are direct coupled audio amplifiers still produced?
A full-H driver for a stepper motor coil does exactly this. They are available as analog types or using switch mode (PWM) drive. Probably a lot less expensive than a Crown DC-300A.

Have a look at this: https://www.robotshop.com/en/simple-h-20a-5v-28v-r-c-dc-motor-driver.html