In my searches, without going with a full blown "car-puter" (as they're called), there is no way of having mobile FLAC. I guess you could mount a "Touch" in your dash, but you're also mounting a power inverter in there as well.
I've got a unit with a 750GB harddrive ('HDD'). Ths biggest problem with it is load time. To date, I've got roughly 10,000 songs on my little pocket HDD. A mere fraction of the HDD's available space, but it still takes 45 - 50 seconds every time the ignition key is turned on to "reload" the HDD into the head unit. If you load up a couple terrabites, you might as well never shut your key off, as you'll never hear any music.
More power to ya Brother. I'm with you, all the way. I've just not found it feasable with a reasonable amount of money, time to modify the vehicle, or space available in the vehicle to mount the equipment to take my listening room "with me".
Bob