I plan to build a custom fiberglass glovebox and mount a modern DIN radio in it. I just picked up a new Kenwood unit for my BMW that plays CD's as well as MP-3 and WMA files burned on a CD-Rom, so you can stuff several hours of music in there. It cost less than $160. I love it, it makes 50W/ channel and sounds great. The unit has a full function remote control so you could control it with the glovebox shut if you provided a pathway for the IR sensor to run the remote. An alternate location would be under the seat or behind the dash on some sort of power up/down motorized mount so you could make it dissapear.
I plan to mount a pair of Blaupunkt 6" speakers in the front part of the headliner and a pair firing up from behind the seat. A small sub under the seat would create a pretty nice system. Just use dynamat to control the noise.
I don't mind things showing in the interior as long as metal wasn't sacrificed to do it.
