If you choose to switch to an in-car-computer system, the sound quality and the drive shock protection will be the least of your worries. I think your concern will be mostly with the reliability of the various PC components and with the usability of the software.

Anyone can slap an LCD and a hard drive onto a computer board and make a car MP3 player. It's the features and the reliability of the empeg that make it so good.

To answer your questions directly:

The empeg's output DSP was made for high quality car CD players and in theory will sound better than a PC sound card. But the difference would be minor.

The empeg's hard drive shock mount mechanism is custom made, so you won't find anything like it off-the-shelf. But with a little work I'm sure you could fashion something similar on your own.

So you could do the car-PC thing, yes. The question is whether you can do it without it being a mess of ground loops, without a bunch of components failing due to heat, without nasty pops coming through your amplifier when you turn it on and off, without having to wait two minutes for it to boot up, without having to struggle with software that wasn't designed for car use, and without contstantly wishing for some of the empeg's features.

Why are you considering switching to a PC?