So you are only going to use it as a sub amp?
Since it only has 250W sub output (as a 3-speaket system), only 1 Kapa is needed.
Just ensure the sub(s) is(are) wired as 4-Ohms or above. There are many sites that explain how to do this.
[In summary, series connections ADD resistances. Parallel connections reduce resistances - eg, two parallel 4 Ohms = 2 Ohms, 4x parallel 4 Ohms = 1 Ohm.]