I may as well put in my two cents. We us a Forrest stacked dado set, and metal shims.
We have a stack of "templates" made from MDF with dados cut in them.
Since we buy different brands of plywood, and they all vary in thickness, we put the template on the edge of the plywood, (or hardwood), to see which one fits properly. Each template lists which stacked chippers to use, with which metal shims. It took longer to write this than it does to actually do it.
A hold down is required, as the plywood may have some warp to it. We also use the table saw for stopped dados, by putting a pencil mark on the fence, marking where to start, and where to stop. We prefer the table saw mainly due to the dust collection system.
As far as getting a straight cut over an eight foot length, we use the ezee-feed device, so that is not an issue. Not meant to be a plug for ezee-feed, but it does make it easy.