There's actualyl rollovers on the labels for them ... It's basically a terrible UI, but by the time I get to adding options to that options panel I just want to go to sleep

So Rebuild-on-PC means that you want the computer to construct the database and send it over. Only checking rebuild-on-pc means it will do it the "safe" way, which is to enumerate all the FID files on the Empeg one at a time, loading the tags in and building the db file. This is REALLY REALLY slow. I'm not sure there's even any value in keeping that implementation at all actually except that maybe someone could come up with some clever optimizations (some sort of hijack interface where it will stream all the FID files concatenated together).

So Fast Rebuild is a variation on Rebuild-on-PC -- in fact it requires that you turn on PC rebuilds also. Instead of downloading the tags from the Empeg, it takes advantage of the fact that it already has the entire database in memory and just vomits it into the Empeg database format and ftp's it over. It's REALLY fast. The catch here is that if there is some wacky problem, like jEmplode is out of sync or who knows what else, you might get a wacked database. It's probably pretty safe though. And worst case is to blow about the database and just let the Empeg rebuild.