Prova con qualcosa di simile: fai attenzione in particolare all' ultimo if!
Codice PHP:
        string currentChannelLink,currentChannelTitle;
            while (
reader.Read())
            {
                
                
XmlNodeType type reader.NodeType;
                
                if (
type == XmlNodeType.Element && reader.LocalName == "channel")
                {
                    
currentChannelLink "";
                    
currentChannelTitle "";                    
                }
                if (
type == XmlNodeType.Element && reader.LocalName == "title")
                {
                    
currentChannelTitle reader.ReadInnerXml();
                }
                if (
type == XmlNodeType.Element && reader.LocalName == "link")
                {
                    
currentChannelLink reader.ReadInnerXml();
                }
                if (
type == XmlNodeType.EndElement && reader.LocalName == "channel")
                { 
                    
//a questo punto hai il title e il link del channel
                    //e componi l'output
                
}
            }