Greetings ! I was planning to buy Yamaha RX-V650 receiver. However, I doubt that I will have 7.1 speakers in the near future (due to limits of the room). Now I'm thinking about Yamaha RX-V550 (6.1). What are the differences between these 2 models ? Is there any feature that 550 doesn't have compared to 650 ? Furthermore, is either of these 2 models overkill for JMLab Sib & Cub2 5.1 speakers ? Should I look for some other speakers ? Thank you in advance !