OHM's in speaker system

Hi all forum members, I own a Sony multi channel AV receiver (STR-DN1010) operating through a 8ohms speaker system, I am not impressed with the receiver, and thinking of purchasing something from the Onkyo range, but these operate through a 6ohms speaker systems. Does it mean I would have to exchange all my speakers to accomodate 6ohm's. ?

Going back to my Sony AV/Receiver, I am having trouble to set up the system, I use to have it working through a 7.1 speaker system, but after my front room alteration,I have to return to a 5.1 speaker system, since the change I am having difficulty to set my surround back speakers. I have attempted to set up via Auto &  I have attempted to set up manually, but no luck. I would be very grateful for any responses or advice ?

Awaiting your replies, thanking you kindly.

Regards :- FROGIT