I don't think there is much heat coming off the scanner. Not as if there is a big honking audio amp or anything in it. I have a 996 and 15 stacked in ISO mounts for the last several years and there are no issue.
I suppose if you were to chose and your stereo is fairly high power I would just keep the stereo on top so if it is a little warm that heat does not effect the scanner.
I also had the 996 below the stereo in ISO mounts on the previous install, no issues detected.
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