So, if you had track number information in the filename when you uploaded it, it'll be gone when you download.

Only if you didn't put it in the ID3 tags, or didn't fix it up on the player itself.

emplode formats the filename as album - tracknr - artist - title.mp3 (or .wma). You can use Tag&Rename or similar to put the tags back from the filename.

Any tags that were in the file originally are preserved. Any changes you made with emplode aren't written to the tags, just to the database.

So, it's only any good for retrieving those tags. If you're bothered at all about the other tags (and I'm not, with the possible exception of year), use JEmplode, it's more configurable in this area.