While tempted by the new HD500 Vieras, I'm wondering if the inbuilt speakers are good enough to be part of a surround sound system. Because of kids, sensitive-eared spouse, etc., we never have the volume up too loud anyway. Is there a way of adding 2 rear speakers and getting 5.1 sound, or is it just going to be crap? It would avoid buggering the room up with satellites, and also free me up to get some really decent stereo speakers... (these would be in a different position to any surround setup, due to plasma having to be sited on a swivel mount in the corner alcove). Ta very much.