I am an electrical engineer; however, be that as it may, the circuits have nothing to do with Kemper being able to use DSP and Impulse Responses to recreate both pedals (FYI old drive pedals are pretty simple circuits).
I don't want to openly disagree with ckemper and what he is saying (his exact wording), but to be a little more abstract here, a combination of IR and DSP could easily cover more than just a class of circuitry .... it can cover a CLASS OF SOUNDS.
It is a very different way of looking at it. All of the discussion in this thread has revolved around the time domain signal (voltage vs time) ... as in the sine wave images shown. DSP is done mostly in the frequency domain using a digital process called a "Z transform" (feel free to look these up if you really really want something that will make absolutely no sense at all when you first read it).
The KPA is a virtuoso of non-time-domain processing in combination with simple controls that tweak the control diagram (look up system processing diagrams if you want to see how this looks).
It is not surprising to me at all that Kemper did not use a traditional algorithmic approach by modeling each stomp. In a Kemper, it would be totally non-sensical.