It's not that you can't split rails or whatever, it's that the combinations you're trying to get need switches that have more contacts than anyone currently makes. If you want to pull out your electrical engineer hat and design a 5- or 6-pole 5-way switch, combined with a 4pdt for splitting, you could get there. But the parts physically don't exist.
The modern artists pulling off split modes don't have setups like this: they'll pick 5 sounds they actually use, put them on the 5-way, and then maybe have a switch for splitting. When you're wiring something, try to think about the sounds and positions you actually use regularly, and have them be the quickest to access. If there's something else you absolutely need, then add an extra switch, but if it's not necessary, leave it out. It's just gonna get in your way.
I'm not gonna tell you to get an Esquire, but I'll say this: go to a guitar store, get an HSH ibanez, a Tele, a LP, and an SSS strat. Plug them all in and try every position for at least 3 minutes. Take notes on what you liked about each one and why and what you'd use them for and whatever. Then make an informed decision about what sounds are essential for you and you need on quick access, and make those the ones available on the 5-way. If you desperately need some other position, then consider adding it to the switch, but I'd recommend giving yourself a week or so to play around with it before you do that, because you'll be able to get a feel for how you use each position and whether you're actually missing anything.