Glad I'm not the only one fighting this battle.
Working on a set of cabinets that's almost 90in high X 20in deep. Did a lot of staring at it wondering how to make an accurate/clean crosscuts on the 96X20 sheets I had after ripping them on the table saw.
I finally threw up my hands and spent some money. I do enough of these big cabinets (as a hobby, not a profession) that I felt it warranted to spend some money (more tools, more better, right?). I got the TPG Parallel guide system for my Makita track saw, and that does appear to be the answer for my needs. It's absolutely dead on accurate/solid (assuming, of course, that you set it up right!). It also killed two birds for me, after cutting the 90x20 sections of plywood, I then needed to dado them to take shelves. Running that through my table saw sounded "not fun" but with the track and parallel guides, I can just run my router along the track using a guide. Nice and easy, and, because of the TPG system, also, perfectly parallel cuts (I ganged the two sides and routed in one go).
The other option that I've looked at and considered over and over, but simply cannot justify, is a radial arm saw. The Original Saw company; looks like a beautiful piece of equipment, 24in cross cut AND dado blade capacity would work for just about any use I have where I need an accurate cross cut or dado placement. But ~6K delivered, plus the space required? And getting rid of my miter saw/miter saw station would hurt too (no need for both of them).