When I talked to Diamond about this I was told that they deliver 1-piece slate tables with the rails and aprons already assembled. The whole assembly weighs about 900-1000 lbs. and half of that is too heavy for one man on stairs and doesn't fit if there are any curves or angles. Even if you can fit two men on the lower side it's still too much and it's hard for them both to get a good position on it and a good grip. That's why they only install 1-piece slates on ground level, so they can wheel the whole assembly in on carts, at most having to deal with a few steps here and there.
The 3-piece slate tables can be installed above or below ground level. On my 8-foot Pro 3-piece table one piece of slate weighs 250 lbs. and two men can handle that even though it's still pretty awkward.
You need a pro installer to set up your table anyway so why not just contact the best in your area and see if they want to take on the job of setting up a one-piece on an upstairs level. I assume they would be able to judge whether it could be done or not based on your specific situation. If you're planning on doing it yourself, I'd forget about that for more than one reason.
Mike
