Well, we just got our rig back from Mark's Audio in Irwindale (shameless plug!), and they did an absolutely AWESOME job making & installing another pair of speakers for our rig. We didn't want them on either side of the dash -- too much separation up front for us. I'd seen another post about the box that was made, so I printed it out & took it with us to show Justin what we wanted. He came through with flying colors! And the box is easily removable and unpluggable if necessary.
The box is covered in the same kind of material as our dash, and the speakers are 4X6" ovals. They put out great sound! We're looking forward to lots of good tunes as we trek on down the road!