As for a Epia or ITX or P4 ITX (Google them you will see) some of them would fit in a DIn sized dash in fact a few companies make a Din sized carpc (Google again) I would think that cheap onboard sound would suck compaired to the EMpeg but even that can be fixed with a USB sound card.

P.S. I had a Lilliput touch screen and a EPIA m5000 itx board the sound did suck and running Media engine on XP home switching songs was annyoing aprox 2 seconds from switch to play, bugged the hell out of me.