Would it be possible to get some info on the differences between the threading options?  I don't see any mention of them in the User's Guide forum.

Multi-threading was discussed in the CFSM ReleaseNotes.txt for version 1.5.2.2 to 1.5.1.8.  In a nutshell, using multi-threading speeds up the full rescan, and repair of your song data.  Here's an excerpt in case you missed it:

1.5.2.2
- final multi threading build (thanks to everyone who helped with testing)
- multi threading selection can be reset any time in 'Settings' tabmenu
  Note: In testing the use of multi threading improved CFSM performance by
        10-30%, i.e., the total CDLC rescan time was reduced using multi
        threading.  Also, system Task Manager showed better balanced CPU core
        usage.  Your individual results may vary.  It is left to you to test.

Give this a try:1) CFSM>Settings tabmenu, press the 'Reset Threading' button 2) CFSM>SongManager>Rescan Full, or    CFSM>ArrangementAnalyzer>Rescan Full, or   CFSM>SongManager>Repairs>Run Selected Repair Options3) If you have a multi-core processor then you will see something like this message:

NET Framework reports that you have a (coreCount) core processor ...
Would you like to try running the CFSM repair options using
the new multi-core support feature?"

Repairs can be made using the old method if you answer 'No'
Please send your feedback and 'debug.log' file to Cozy1.

Threading selection can be reset in 'Settings' tabmenu"

We will add something to Official CFSM Guilde about this later.

Thanks for the info, and all the work you do.  You're a star!