Designing Kitchens and Bathrooms - Remove or keep concrete slab?

Hello DIYers,
I'm remodeling a small (~5x7') bathroom on the second floor of my 1950's split-level home. I removed everything down to studs and subfloor, and don't know the best way to prepare the floor to install a new bathtub, tile, sink & toilet.
The subfloor is made of 1x6's nailed perpendicular to the joists. The old tub sat directly on the 1x's. Everything outside the tub consists of a raised (~2" thick), poured concrete slab, on which tile was set in a thinset mortar (tile is removed).
What I'm wondering is – should I keep / alter the slab to accomodate a new tub, or should I bust it out and overlay plywood and cement board everywhere?
I'm not worried about the demo. work, but not sure if I'm ruining a good set-up and creating more problems.
Any ideas?
Thanks a million…

Well, I guess you have to ask yourself if you would be satisfied with a 'built-in tub' the way the old one was with a 2 inch (or more, counting the tiles) build up outside the tub. The decision is yours I guess. I would also be concerned as to what all the banging around up there might do to your ceiling below. If the house is ancient and has old plaster walls for example, whacking away up there with a sledge hammer might cause ceiling problems.

But then again, with the tub out of there and then being at the 1 x 6 level, maybe chiseling out the cement would be the way to go.

But if you remove all of this 2 inch cement, then obviously you will have to trim out with perhaps even taller baseboard, or, have wall repairs down there and repainting. But, in remodel jobs you have to crack open a few eggs to make an omlett.

Thanks – I think I'm going to try to "carefully" bust up the concrete and get the floor built back up near the original level*with 3/4" plywood, wonderboard and tile. This is probably also a good opportunity to expose more of the plumbing and replace the old galvanized pipe…

You can rent an electric demolition hammer at thre tool rental centers with a 2" spade, That will get the cement up pretty quick with minimal dage to the surrounding walls and ceilings. Under the cement you most likely will find wire lathe stapled to the planks. After you get most of the cement out the exposed wire will come up with a long prybar. Wear heavy gloves and goggles.