As I understand this situation, usually you need only one xs file which will be a glue between perl and a big set of *.c or *.cpp files.

As examples of distribution with many *.xs files are libwin32 and Tk (perlTk), so you can use them as examples of how multiple xs are processed. I beleive there is more than one xs file there only because there are many independent distribution pieces.

Courage, the Cowardly Dog