Yea so it has to be like normal NURBS, where the mesh object is treated as a NURBS suface...

Anyway, the quad cage construction of a NURBS objects, can't you have any number of points on each side of the quad? Like when you make a sweep?
Or did I get something wrong?

Sounds like Max's patch modelling is actually simplified NURBS, but I thought the big advantage of NURBS was that you could define each side of you plane with more points and make it blend with 2-rail sweeps...

And I don't understand the problem with it having to be 4-sided if you can have multiple points on each side of the quad, but you can't??

If you read through the thread I linked to before, you will also find an example where it is shown that Maya can make a sub-D with 3, 4, 5, 6, and 7 sided polies, which is converted to NURBS afterwards, but he also mentions some odd cage topology, so I guess Maya has some special algorithms to handle that.

I wonder if Max's NURMS (Non-Uniform Rational MeshSmooth) is catmull-clark sub-D....