I totally agree. I think that "on-line/off-line" switch on emplode would just be perfect. You could create a mirror of the empeg content on hdd and manage it via Emplode, and have emplode take care of sync-ing the two (three, four?) locations, at your request.
I can imagine a set of simple options saying

Locations A, B
1) Mirror A on B
2) Mirror B on A
3) Ask user (file by file, or playlist by playlist)

Etc.