After following S8_UK advice, and in spite of having bought a second cartridge with 40 Gb, I decided to hack my Kenwood Music Keg -FWIW the head unit is a Kenwood too-
So I downloaded Phathack DMS Tools, run the hack wizard and installed the hack in the old, 10Gb DMS cartridge. The wizard said the files were copied, I ejected the removable media and followed instructions.
Inserted the cartridge, switch ignition on, head unit selected to "CD changer", and the process started. After six or seven minutes, the unit started playing what used to be the first song of the first disc. After 10 minutes I switched the ignition off.
What startles me is that, when inserting the DMS back in the cradle and run the Hack wizard again, it says that either the installation failed or didn't started at all, as it couldn't find the log file. But the pahthack tracks played... and, after all the process was done, I inserted my second DMS cartridge and it played as it should.
So I don't really know whether the hack suceeded, or didn't run at all. How could I know?