You guys are legends.... Big thank you. Here is what I did to migrate my library set up over to Linux. I am just used to looking at my music library sorted by date of import since I am focused on new stuff I am importing/cleaning up as I import. I roughly know where to scroll to find stuff on this view I have had even since itunes days. I know the other views are still there for artist etc. but of course they wont be impacted by a rebuild.
1/ Restored library + Settings, quickly turned off/deleted entries for Auto-Import [Should really be a check box for this on the restore dialog? Everyone seems to have to diable quickly otherwise it messes tags up..]
2/ Selected a handful of files.
3/ F6-Rename/Move/Copy - Find&Replace setting only (Filename, Directories unticked). tick-Convert Windows paths syntax, Find 'M:', 'Replace with '/home/user/Music' the mount point for the whole media library. tick-Replace slashes in expressions [not sure I have any expressions though-calculated fields right?]. Created a Preset for these settings called "Linux Media" so I could come back to it.
Original trial did not seem to replace the front directory. So I went in to menu, File,Library,Portable Library can created an entry "M:|/home/user/Music" then tried again. It may have been another setting that I change cant remember - until the 'Preview pane' looked correct. Ran it.
I noticed the tags had successfully changed the path name of the file - but the library still marked the items as broken links. So I took a punt and tried with the same selection - menu Tools, Library Tools, Update Library (from tags) hoping it would process the selection not the entire library which it did. Success!
4/Ran a couple more trials using the Preset in F6-Rename/Move/Copy so the settings were exactly the same, then selected every file in the audio library and let it run overnight. Next morning ran the Update Library (from Tags) again over the selection.
5/Repeated the same for all pictures and videos files also.
I notice a couple of learnings... The F6-Rename/Move/Copy provides no feedback after you hit OK and it returns back to the library view. I didn't know if it had finished or if I could remove the selection. Compare this to Update Library (from Tags) function which provides the "updating file x of y" in the staus bar as it goes. All in all rather painless and far better than letting Auto-Import remove all broken linked files, and reimport everything again.
Besides that I also directly copied my custom standard view skin (Dark black with LP Groove pictures in background) to .jriver/Media Center 30/skins/Standard view. In addition to playing around with a better display font that "Sans" which must be the default... and I was all back up and running. I think this ONLY worked because I have been diligent in storing clip art in the actual media files (not a folder) AND breaking up albums to individual files (ie. no cue file) by convert audio format eg. Flac -> to Flac then removing cue file & all -in one-album files. Milage may vary for others who have not done this as it will look like blank cover art and/or duplicate audio files.
Thanks Again!
A Footnote: There were ~10 albums I had to rename folder names due to mismatch capitalisation. Items where the file name tag had a path that contained "The" where the actual folder name has "the" therefore not a match in Linux but functions in Windows since it ignores capitalisation. Not an issue for Media Center but Windows. The good thing is the way to find these is via the files display and display "Image File" field and see items that are not 'inside file' or 'folder.jpg' that I have some of the old MP3 still as. Even if you copy paste the cover art back to the tag or look up from internet - it does not stick and save inside the file. This issue should be expect ed from anyone migrating library to Linux set up.