Happyhiker's method is the usual way of dealing with it, though at 21ft square, you might well need a more powerful amp! The speakers on any plasma are gonna sound like a penny in a tin bucket in that space, you need something to kick butt in there. How about running the wires outside? Any possibilities? You also need to think about wiring to the screen if it's wall mounted. If this is all retro fit, it makes things harder, but not impossible. All sorts of tricks have been used, often in conjunction with a cupboard for the electronic side of things, amps, DVD players etc. I'd scratch your head for a way to get some speaker wire, not to mention a sub cable, into that room. You can get flat cable, and micro sub cable to help you. I assume this is a wood floor, or I'd be under the carpet like a rat up a drainpipe. I have been known to glo-rod speaker wire inside coving, but it wasn't easy, depends how the builders stuck it up.