My interest is not tied to any particular hardware but the concept of accessible music.

In that case, yeah, you can assemble lots of off-the shelf parts and make a car computer that plays MP3s. Others have done it, there have been many discussions of those sorts of systems here on the BBS. None of them, so far, has been better than the empeg in terms of quality, convenience, durability, and usability. The empeg is the ultimate end-result of taking that idea ("what if I used a hard disk to store music in my car?") to its logical conclusion. Any frankenstein system, although functional, would fall short of the empeg in terms of the purest execution of that concept.

I'm sure the empeg guys are working on taking that idea even farther and making it even better now.