Well I guess the obvious thing would be to replace your old Panasonic (and I'm assuming it was a home cinema in a box system) with another one from Panasonic.
Unfortunately the only Panasonic model we've tested recently, the SC-RT70 (£600), scored a very mediocre 2 stars. Not good.
We do, however, have a test of new home cinema in a box systems coming up in the October issue of What Hi-Fi? Sound and Vision, on sale August 23, so you might want to get hold of that and check out the latest models, although they do all come with their own speakers.
The other alternative is a system such as the Pioneer DCS-353, which is really good and only £279, or the Sony DAV-DZ210D (£280). Depends how much you want to spend.