Can your stereo save already compressed and tagged mp3 files?
or is it like the Sony's MEX-1HD that will only save Sony's unique ATRAC3 file format to it's internal 10gb HDD.
The whole thing with the two Sony units was that the relationship between Sony's product people and the record company they also own is sorta like performing auto-fellatio while a team of lawyers and Doctors advise them to use a rubber to prevent catching a disease.
The whole thing was so handcuffed by their own desire to make it capable while maintaining DRM integrity that it was doomed to fail in the market place.
I am not familiar at all with your particular unit nor do I see enough information so that I can research it (to read the manual myself)
and then offer suggestions.
Frankly I think the whole point of an internal HDD or SSD inside a stereo head unit became moot with the introduction of stereo head units that have either a direct BACKPLANE interface cable to slave control an iPod OR a USB cable to control some other portable audio device like it was any other plug-in accessory (like a CD changer)
That and "Multi-media" decks that'll play a DVD Disc filled with mp3 files like the Sony MEX-DV2000 or similar.
4.7Gb on a removeable optical disc beats a 1gb internal HDD
and would give a 10gb HDD that would allow open source audio
files (mp3's) a run for it's money.