I don't think there is any nebula program processing frequencies above 20 Khz .
if you sample at 96khz the tone goes up beyond 20k. i believe it always goes to nyquist. you can see in some freely available programs that were done with consoles (like alexB's TFT Pro demo) or preamps, that nebula does still process stuff up to 48khz, when using 96k rate. whether that will effect anyone's perception of anything is another question.