Unfortunately (and, I think, surprisingly), filename isn't used by sync to determine sort/play order (I tried that first :-)). Once you are in an "album", it relies next on track number alone, which for common 2 disk sets means I get something like mvt 1 of a symphony (first track on first disc) followed by movement 3 (first track on second disc) then movement 2 (second track first disk) and so on. It's not pretty.
Ultimately, I am ok with mangling the meta data, because I have to make copies of the files anyway. My source files are all FLAC, but sync wont play flac, so I convert them to wma. The meta data I'm changing is in these copies.
I add music to my source collection (the master) and tweak tags all the time and don't want to keep up with it on a separate copy, so every once in a while I like to just wipe the hard drive with the copies, re-convert all the files and copy them over fresh. The problem is that there is so much tweaking required AFTER I copy to the hard drive. It is the tweaking that I am trying to automate with custom expressions and tags.
I've been tempted to just write a program myself to handle this process, but I can get 98% of the way there with existing tools, I just need to close a couple of more loose ends and I think I'm there.
Thanks again for your help.
Dan