Pull info from XML doc and match with another in PHP

I have one XML document that list clients with clientid, then another that list servers based on the client id. Is there a way in PHP to pull the one in and list the clients and then pull in the servers from the second all in one swoop. What I am doing now is loading the one, then linking to a second page and passing the clientid over to a second page and pulling in the info. I tried with simplexml_load_file and the looped through calling simplexml_load_file on the second document once per loop, but it was VERY inefficient and will bomb out when I add a third tier later on.

Any thoughts, suggestions, links to tutorials or anything like that would be greatly appreciated.