All the stair jigs I've used were designed to use a guide bush and a stair housing cutter (like the oversized dovetail cutters I highlighted in a previous post). I use the Trend jig myself and it comes with an auxilliary base plate to fit to the router (also comes with an alignment pin and a centring bushing). Fit the sub-base, centre-it on the collet (same as you would for any jig operation, really), fit the guide bush, fit the cutter, set the height and away you go. It's not a plunge routing operation, BTW.
Looking at the Model 7 you refer to, the kit clearly shows P-C guide bushes as being supplied with it (bottom right of the photo):
View attachment 1
So providing that you can fit and centre a P-C (Porter-Cable) type guide bush you should be OK.
TBH, though, I think that is a grossly expensive way to do a one off, or even a few different stairs. It is a massively over engineered CNC cut steel production jig. You know, it is completely possible to make your own jig using plywood, a framing square and a pair of buttons and as a joiner I have done so quite a few times in the past. It would also save you hundreds of dollars to spend on more Festool tools....... Personally I eventually went for a mid-market Tufnol (cloth re-enforced phenolic plastic resin) manufactured jig because it was becoming too costly in time to make a new jig each time, but in reality it really only takes about an hour. I still do 2 or 3 stairs a year from scratch - on that basis my jig will last me until I'm about 300! Making the jig will also force you into thinking about how and why things are done the way they are in stairmaking - no bad thing when you get involved in structural stuff.