It almost looks like the long list of PK_Files is the subset of media files of the particular MediaType that the data grid is to be for. eg all the media files of "LinuxMCE Video File" type, so the query only returns video files.
That doesn't seem very efficient (intuition only here!). If that is the purpose wouldn't it have been better to have used the EK_MediaType key in the pluto_media.File table and just use a normal matching Where clause?
Or is that set of PK_Files something else entirely? hmmm.... perhaps it is the subset of files it has determined are currently "available" based on which media sources are currently online/connected to the LMCE network?