I'm thinking of buying an Onkyo TX-SR505 AV reciever (I believe this is a good choice at the price - although please comment) but I'm not sure what speakers to put with it. Does anybody have any obvious suggestions? My budget is £300. Alternatively, I currently have a pair of Wharfdale delta 30's and a pair of Goodmans Maxims. Could I just purchase a sub and centre and get reasonable results or do I really need to buy the whole system? Any advice would be much appreciated.