The only thing I'd be worried about with splicing it straight in, is the problem of constantly getting clean power to the Mini. Though it makes less sense to step up the voltage only to have the PSU step it back down again. Maybe a 12V power filter could do the job. I'm sure I could build one up with little effort.

I might ditch the Mini idea completely after thinking a while. I've got quite a few spare Macs lying around that can do some good getting put into action. Besides, such a powerful machine would do much better under my desk than in my car.

So this is the part of the thread where I take this in a completely different direction.
(I still have the 8500 coming, so I'll make something fun out of it. Or soup it up or something like that. But I'm changing the parameters.)

I have a PowerBook Pismo, fulling working and upgraded laying around with nothing to do. It wouldn't be too hard to build the Pismo into an LCD monitor case (or the like) with a built in USB IR receiver, and mount that in my car with a nice paint job. It would be a a lot cleaner, with a lot less cabling and power needed. Not to mention a lot less modding of my actual cars dashboard (Fun, but not in an 04', when I'm unsure of my abilities.)

Another problem... It seems that AMP's creator has ceased development and shut down his website. Still have 1.4? :-