Eric, did you ever figure this out? I'm trying to do exactly the same thing you were. I want the KM-Z1 to power up when the rest of my equipment turns on. I have the standard 12V trigger available, but I'm wary of just sticking it in either the XS-8 or SL-16 ports and just hoping for the best. I even tried talking to Kenwood support. Nobody there could tell me anything about either the XS or SL protocols. They say they've been out of the home audio business for so long that nobody there knows it anymore. That's disappointing.
What I can gather from reading old Kenwood manuals is that the XS protocol was fairly simple. The SL protocol was more advanced. My guess is that XS was a simple voltage signal to turn on. SL was probably a digital signal, possibly two way. So my GUESS is that the XS port is hooked up to a simple relay, and applying any small DC voltage across it should do the trick. If that's the case, the everybody-but-Kenwood standard 12V should do it, and it should be as simple as plugging it in and crossing my fingers. But I'd sure hate to fry something if I'm wrong.
Anyway, I was wondering if you ever figured it out. Or if anybody else has some experience with these Kenwood signal protocols. Or if anybody is still using some equipment that has these ports and could take some quick measurements for us.