Hi bartosh44.

Well...there many ways to do it.

If you want, at any cost, doing that all inside Moi, one of the ways is like AlexPolo said.

I've made a brief video example of what I'm talking about.

Is a simple use case where I have a very simple polygonal cage made in some Poly/SDS software, in this case Rocket3F, and I export it to Moi.
Than in Moi I first apply Max's subdiv and then I do a "downgrade" of topology of the resulting joined surface.

Clearly this method is good only if you don't need to exactly match the starting surface, but you can accept a certain degree of approximation.

You can watch it here : http://take.ms/diY5A

Anyway...this is a very time consuming method and I think that all should be done more easily in Poly/SDS/Sculpt environment as Michael said.

But, if you like it, consider this as a alternative way.

Bye!

Marco (mkdm)