I think you're the first person who has said that they prefer the empeg player software over a piece of PC software.
I mean, not to put the empeg player software down or anything, but it's meant for a very limited input interface on a small screen in a car. For that situation and environment, it's the best available, hands down. But for in the home, the larger screen and mouse interface available on desktop PC's can do so much more.
You've got an interesting set of requirements for your home player, the massive storage being the trickiest. But have you looked at the Rio HSX-109? It's designed by the same people who did the empeg-car, and the software is very similar. It can only fit a single IDE hard disk, though, how big do they make IDE drives these days?