If you consider how many Empeg/Riocars were ever made, I'm troubled to see so many get stolen or otherwise end up in the wrong hands, so here's an idea.
There's a good chance the new user (carefully avoiding the word owner) will at some point connect the unit to a LAN with access to the outside world. What if, every time the Empeg connects, it sends out a small email (or tries to) to the rightful owner so it can be traced through IP address?
This assumes that the LAN connected to has a gateway directly to the internet. There are free POP3 email providers that use an SMTP server that can be accessed from anywhere (myrealbox.com, for instance; can be accessed as webmail too) so should be easy to set up.
I know this suggestion wouldn't do if only used with USB or if LAN uses a proxy server, but even if 30% can be traced this way without the offender realising it, got to be a good result.
The disadvantage is that your Empeg keeps sending you mail whenever it connects anywhere, but I suppose that can be easily filtered by an email program to send to a separate folder so you don't need to look at it unless there really is a problem!
Note that in my fantasies I'm not hindered by any knowledge whatsoever... Comments?
Cas.