That PEK file is not an edit file, it is a temporary "generated" file used internally by the program
Bottom line..... if you want to import the Copied Folder's audio exclusively for playback as a music file, you use the copy of the music file itself in the Copied Folder and not its conformed audio files (cfa and pek) of which the pek file is one (involved in the project'sTimeline waveform). You do not use cfa and/or pek as a playback audio file.
When you write
In the BDMV folder, 00000.m2ts represents the movie file; 00001.m2ts represents the main menu of the disc menu; 00002.m2ts scene menu
What you wrote tells me that you are trying to play back a standalone conformed audio file that relates to a main menu replacement audio in a disc menu. The replacement audio has 3 possible files associated with it, the audio file itself (Project Assets, .mp3, wav), the conformed audio set of cfa file and pek file (Media Cache Files Folder). The pek file is related to the waveform that you see in the audio track display style that displays the audio's waveform in the project.
If you have imported audio to the project's Timeline and have replacement audio in the disc menu, then in the Copied Folder you should expect to find
IN EACH CASE 3 files - the music file itself and the associated conformed audio files (cfa and pek).
If you remove the .pek file from the Copied Folder, the project.prel that you open from there will have audio issues (no audio track display waveform and
probably no sound). The program automatically generates these conformed audio files if deleted, but.... that is another story.
You are not looking for a .m2ts codec.
I did not see your reply to John numbered 2.
Please refer to my full description of your situation in post numbered 3. If any questions, please ask.
The file I was looking for was in the Archive (copy) located in a folder and Premiere Elements apparently could not find it.