OK, the new radio should come with a metal bracket that you can put in there to keep it in place (mine is basically supported only on the front with the tabs on the metail rail; this is not ideal, especially for offroading, but I did not have a choice) and I would imagine that the TJ's have the metal tab on the back to hold the stereo in place.
This is the metal bracket:
Once you have it in the hole, flip the tabs to lock it in place like this:
Because your Jeep will most likely see more bumps than the average car, you will want to make sure to use the rearsupport if you have it (my YJ did not, but check ayway's in case it does; if itdoes not have it, try to support the stereo with something beneath it so that it will not break if it hits bumps):
Also, since you had a Sony radio, the Sony wire color code is like this:
(In case it is not visible, the speaker ire color with the black line is the negative for the speaker)
Hope this helps, and I hope you replace your stereo with a Sony once more!
Felipe