Oh and Seph, if that question was directed towards me... I have the stock sound system, not any of the Mach systems. I had my old cd player in the lower din slot in those pictures, but I actually just sold me old headunits (tape/radio & cd player) last week so I had to remove it. I'm holding off till Zim finishes his switch panels and then I'm going to get one of those to fill it in.
Your other less stylish but useful approach would be to go to http://www.stangparts.com or a Ford dealership and for $25 you can get a little storage compartment that goes in the empty din slot.