That is a really cool setup for a garage. I personally keep mine cheaper and simpler:
I keep all of my music stored on my computer and run the computers sound through a vintage tape/radio stereo receiver that I picked up at goodwill for about $10. You can get lucky and find some pretty powerful receivers for cheap.
I just run the audio out on the sound card of the computer via a 3.5mm stereo jack/stereo RCA cable. The stereo RCA cable plugs into the aux in on the receiver and the receiver powers my speakers in the garage. Sound comes out of a set of speakers each equipped with 2x12" drivers with a 4" mid and a 3x7" horn tweeter. Got them for $50 at goodwill as well. Gets loud enough for my neighbors to enjoy Iron Maiden with me if I want to be "that guy" when I'm working on my '65 and I don't have to fiddle with any cd's or ipods or any of that junk. I just play it through winamp on the computer.
i do the same, but everything, including the laptop, came from the local dump e-waste bins. its amazing what one can find that others see as garbage