Q: connecting dimmer,8A to high power white LED strip ?

I have RF dimmer that can handle 8Amps from Ebay.
I must dimm 20meters of WHITE LED strip with that unit . thats around cca 250 W , cca 21 Amps

How to do that ?

I saw in my friend caffebar, he has simply RGB Amplifiers somehow connected that dimmer can handle that current.

Maybe can someone tell me how to connect that RGB amplifiers ? Or maybe there is somewhere some schematics on Internet where it is described what to connect ?
I saw that input pins of RGB Amplifiers are somehow short connected - R with G or similar :S

Thanks !