Vlad,

My action code is:


public ActionResult Write(string data, string format)
{
    Ext.Net.SubmitHandler submitData = new Ext.Net.SubmitHandler(data);
    XmlNode xml = submitData.Xml;

    MemoryStream m = new MemoryStream(System.Text.Encoding.Default.GetBytes(xml.OuterXml));

    XPathDocument xpathDoc = new XPathDocument(new StreamReader(m));

    XslCompiledTransform transform = new XslCompiledTransform();

    StringBuilder resultString = new StringBuilder();

    XmlWriter writer = XmlWriter.Create(resultString);

    transform.Load(Server.MapPath("~/Content/Excel.xsl"));

    transform.Transform(xpathDoc, writer);

    var result = new FileContentResult(System.Text.Encoding.Default.GetBytes(resultString.ToString()), "application/vnd.ms-excel");
    result.FileDownloadName = "Test.xls";

    return result;
}
At the moment I am only working with transforms to excel but once this is working, would then modify it to work with all three types.