I use the SparkFun ATX Power Shield to control the 6 PWM LED channels.

SparkFun Power Driver Shield Kit

Code snippet for controlling the ATX shield

/*
 ATX shield with ATX control
 claude felizardo 2018-08-06
 
 https://www.sparkfun.com/products/10618

 Uses modified ATX shield to use pin 2 to control PS_ON control pin on ATX connector.
 */

#ifndef _atx_shield_h_
#define _atx_shield_h_

#define ATX_SHIELD_VERSION "$Id$"

class ATX_Shield
{
    int atx_ctl_pin = 0;    // output for controlling ATX power supply
    int atx_enabled = 0;    // current state

    public:
    ATX_Shield(int output_pin)
    {
        atx_ctl_pin = output_pin;
    }

    void output_power()
    {
        Serial.print("atx_enabled = "); Serial.println(atx_enabled, DEC);
        digitalWrite(atx_ctl_pin, atx_enabled == 0 ? HIGH : LOW);
    } // output_power

    // this should be called once
    void setup()
    {
        pinMode(atx_ctl_pin, OUTPUT);

        atx_enabled = 0;
        output_power();
    }

    int isEnabled()
    {
        return atx_enabled;
    }

    void powerOn()
    {
        if (!atx_enabled) {
            atx_enabled = 1;
            output_power();
        }
    }

    void powerOff()
    {
        if (atx_enabled) {
            atx_enabled = 0;
            output_power();
        }
    }

}; // class ATX_Shield

#endif // _atx_shield_h_