The -KB bonus should only stack 5 times, and in the current version, it looked like it's working fine when i just checked it. (Why anyone'd want -20 KB from IOs i'm not sure, but it'll stack that much...)
However, my understanding is that it's specific set bonuses that cap at 5, rather than the individual effects they contain. So I believe it would be correct to say that you could slot 5x Karma and 5x steadfast -KB IOs and get -40 KB, since their set bonuses are two different named bonuses and aren't counted together for capping.
And then I'd
really be wondering why you need -40KB!
I'd also be begging you for inf, since if you can afford all those, you must be loaded!