Only two "empeg" keys in my registry.
the first is under:
HKEY_LOCAL_MACHINE\Software\empeg\empeg-car

the second is under

HKEY_CURRENT_USER\Software\empeg

But on my system (which did ask for a serial number originally when I first installed it) neither has anything of interest there now
[there are a couple of older keys/values there].

I uninstalled the 1.0 of Emplode when 2.0 Beta came out.

The only other keys to look are:

HKEY_LOCAL_MACHINE\Software\SonicBlue\emplode

and

HKEY_CURRENT_USER\Software\SonicBlue\emplode

But again nothing much of interest in there that looks like a serial number.

So, have a look in these 4 places in your PC's registry it might just contain the serial number somewhere on your system.