Yes! Great that you're already digging in!! Yeah, Max is fun isn't it?
Check the Kemper manual too though. Addressing the higher performances is a bit tricky.
Going from memory here, as I'm not in front of my computer or Kemper, I think the 1-26 buttons when clicked simply send out their value (or rather 0-25, I think, hence the initial "+1" operation). This is then multiplied by five, followed by subtracting five. So button 1 yields 0, button 2 yields 5, button 3 yields 10 and so on.
I may be getting some of the exact values wrong here, but the idea is that each button sends out the Program Change for the first slot of the corresponding performance. Since there are five slots in each performance and every slot has its own PC number, you have to jump by five to get to the first slot of the next one (of course, you could adapt this if you'd like to be able to jump straight to any slot in any performance).
This also means that you run out of PC numbers (0-127) pretty quickly. So to address performances higher than 26, you have to work with higher "banks". This is explained in the Kemper reference manual somewhere. I don't know how to set the bank number in Max, but there must be a way.
Good luck! I won't have time the next couple of days but as soon as I can I'll take a look too.