I intend to change my current receiver to either the Yamaha or Onkyo receiver. The Onkyo model cost extra GBP250. Which of the two should I get? Do you think it will be a good idea to add 2 more speakers to make my current set-up to 7.1? If I decide to go 7.1, I will add either the Wharfedale or Kef as front L/R speakers. Which would be better? What about MS Aviano 6?