Hi Dave,
I was surfing the web trying to solve the same problem you had months ago and luckily found this thread. I just opened my new Keylab 88 Mk II and the first thing I tried was setting up MS such that the pads and keyboard played different instruments each. Yet I am still unable to get the result I want, which, if I understand correctly, you may have achieved.
As far as I know your solution was setting the "keyboard" parameter to "None" under the midi input tab for the drum sound. What I don't get is how you get the drums to be triggered by the pads in the first place!
What I've managed to do so far is to make the pads trigger the drums only, but my keyboard still plays both the piano and the drum sounds. And... even so, I kinda don't know how I got it to work that way. MS can be really confusing, as you said.
So I just wanted to know more about the way you solved this. For example, do you have one only keyboard and an additional 16 pads showing in your layout mode? Is the Keylab's keyboard set to "1-16" channels in layout, or is it just 1 (does that even matter)?