I've seen pics with them behind the center of the dash. However, I could not get mine to fit back there and I was sick of trying to struggle with it in the cold so I just put it on the passenger floor. It is tucked as far on the left side as I could get it underneath the floor mat. You can barely see it, because its fairly out of the way. I think this summer (if I still have my car) I'm gonna try and tuck it behind the dash somewhere. Hope this helps and good luck.
You will need two wire harness. One is of course the one needed to plug and play for your new cd player, the other is a reverse harness. Its designed to plug into your stock head unit. Wire up the harness for the cd player, and tap into the the power wires (red, yellow and black.) Only hook these three up and tape off the rest of the wires, and plug in the green harness which works the keyless entry, as well as your dome light circuit. Pull out the center console and cup holder, you will have plenty of room to hide it back there. If you have the oem cd player down there, you will need to buy a little pocket because it's not as deep, if that's not a choice, then just extend these wires until you find a good place to hide it, this isn't too recommended since you'll have to extend the wires of the green plug as well, more work to do. This way you don't lose keyless entry and still have a better cd player. Hope I helped
anyways, i just bent that blue clip on the right to get my radio to fit in the dash. it's really tight, but i got everything back together and working.
i really don't know how i managed to fit the radio underneath the cup holders, but somehow i did. like i said, all it involved was bending that blue clip out of the way. i wish i would've taken a picture, but i was running late for work as it was.
anyways, thanks for the info. click my civic link in my sig to see the radio installed.