No, you would NOT throw away the speakers that come with the all in one package, because, since it is an all in one package, I'm pretty sure that you would not be able to connect alternative speakers, in your case the Kefs. You would have to dispose of (sell?) the Kefs.
I really think that you should keep your existing Kef speakers, you should save up a bit more and buy a cheap Blu-Ray player (about £80) and a cheap receiver (about £180). Which really shouldn't be too complicated to connect together, if you buy from Richer Sounds they will advise you. If that IS too complicated you'll have to sell the Kefs and get an all-in-one system.