How exactly are you measuring the input power with your multi-meter? Do you know what power factor is? The power monitor functions for GPUs is notoriously inaccurate. What is the efficiency of your PC PSU?
All these things make accurate accounting for power difficult. No way are your CPU and risers and other system components using 680W.
Baz
That's a good point. When you mentioned power factor, I just realized that when I read the power, I activated all machines, which drew interference. After I turned off most machines and left only 1 to be read, the reading said it was around 1760 instead of 1980. I use 80plus gold PSUs by the way.