Softimage have released a new version of their free XSI Mod Tool. This is a cut down version of XSI that can be used with XNA and Valve's Source Engine (such as Half Life 2).
Unlike previous versions of the Mod Tool which required exporting to DirectX .x mesh files to import into XNA GSE, this version comes with a custom importer for XNA GSE that uses the Crosswalk SDK to import .xsi and .dae (COLLADA) files. The processor spits out the usual Model type but includes XSI specific animation data in the Model.Tag member and there is sample code showing you how to use the animation data. In other words, apart from a few rough edges, you can make an animated scene in XSI and then export and view that animated scene in your XNA game.
The Mod Tool has an XNA GSE addon that manages the creation and export of your models into a particular project, including a nice feature to diagnose your model and inform you of any potential problems. It's a little rough but given that its written in JScript it might be possible to improve or customize it to your needs.
It's good to see another addition to the growing line of software that supports the XNA Framework.