Sorry friend but this question, and those similar have been posted several times before, and all our angst about it we know of no way to do it that will retain the parameters.
The best and easiest way to translate solids or sheets from UG to UG would have to be the parasolid route.
However if you need to retain some curves then you'll probably need to use IGES. STEP and IGES are both translators and can tend to degrade the data. IGES will render all of your solids into sheet bodies. So if you need both curves and bodies maybe use IGES for the curves and parasolid for the rest.