The obvious choice for this conversion would be CATIA software from Dassault Systemes, because both .3dxml and .model are from software created by the company. Alternatively you would have to use some of the dedicated 3D conversion software, such as the CrossManager converter.
Convert Dassault Systems Universal 3D XML document to CATIA V4 model file.
We have found 3 software records in our database eligible for .3dxml to .model file format conversion.
Microsoft Windows software - convert 3dxml to model on Windows
A PLM/CAD/CAM/CAE software suite
Convert from 3dxml file format
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned 3dxml to model. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
A CAD converter with huge format support
A CAD visualizaton, analyzation and translating system