From the FAQ

Although it is possible to port the server software to Linux and run it on the car player (someone actually demo'd this very thing at one of the user meets), the database code eats up a lot of memory. So having the player be a server and also having it continue to work as a player at the same time probably isn't going to work very well.

But the hardware spec of the HSX is very similar to the empeg

From a post by Rob on the empeg BBS

206Mhz StrongARM
16Mb RAM
1Mb Flash
320x240x4bpp greyscale (OK, bluescale) screen

CPU utilisation is far nearer the max than with the car player, as this product background rips and encodes.

Rob

So why not?