there are other xpath extensions. of course, if it is written in PHP it is SLOW.
try: phpxpath
generally, when i need to parse data from XML and export it back, i write a class that can both parse in the file and print it back out. if you are building a tree from the data anyway, you can easily turn this back to XML.
personally, i gave up on XML for websites some time ago. MySQL is 15 times quicker and far, far easier to use as a programmer. if XML is a necessity, export it!
if you only need the data for PHP you would be better off with serialize(). it is faster than parsing/generating XML and far, far easier.