martinrrrr,You and I must have been posting at the same time....
From everything I found you can only rip audio cds into music box (Those with .cda extensions). I messed with this for some time yesterday and could not get .mp3 files to load. If there's a way I sure would like to find out.
Regarding the laptop option:
I wonder if there's a way you could use a USB to CF adapter to inferface your laptop into the stereo? I imagine a particular driver might be required so your laptop can emulate a 2Gb CF card. I don't see why it wouldn't work. If the owners manual is correct though you are still restricted to .mp3 files. Even if you could use audio files you can't store raw audio (.cda) files on a computer hard drive.
I'm going to buy a CF card and reader later today. If I can find a USB to CF adapter I may just pick that up as well. It might be fun to mess around with this.