First of all, welcome. I think that with the height of the bed, and your position on it, that you may indeed lose some of the imaging. The higher frequencies are much more directional than bass energies and require a clear "line of sight". If from your position you can see the mids and tweeters then you should be fine. If they are hidden from you then I would be more inclined to go with a bookshelf speaker and sub arrangement. You would also be able to play with the height of the front speakers much more easily and really get the soundstage where you want it. Your best results may come from mounting the fronts at about the center of your screen or perhaps a bit higher.
