Most manuals you read tell you not to place anything on top of your unit and that a certain amount of free space is on all sides. But we've all seen loads of AV stacks just built on top of another. So, is it ok to put, say a dvd player, on top of an amp? Is it vitaly important to have each unit on a seperate shelf/platform? Has anyone here had any probs with stacking their AV units? Also, are there any seperators available to put in between units to give a bit of air flow, kind of like columns on a wedding cake, only not so tall. Maybe an inch or so? Thanks.