It seems that prnx to xls conversion is typically searched by users that would like to export XtraReports files (.prnx) as MS Excel files (.xls). Everything points to the fact that only XtraReports can export its own reports, so chances for 3rd party apps are pretty low. Nonetheless, XtraReports supports many different output formats, including Excel.
Open PRNX file Open XLS fileA reporting tool for WinForms, ASP.NET, Silverlight, WPF and LightSwitch