Is it possible to use the Yamaha RX-V677 with surround wireless speakers? Is there a product which connects to the speaker terminals then sends the signal to a suitable set of rear wireless speakers?
There is something called 'rocketfish universal wireless rear speaker kit' which does this but I only seems to be available in the US. A bit of googling may find a suitable alternative but they don't seem to be a high demand product (probably because you are just adding more mains cables for the sake of saving speaker cables).
The way I have my TV and sofa set up it's actually more convenient to have mains cables for the rear speakers rather than running speaker cables under carpets or round the doors; the mains outlet is right behind the sofa.