“I have an Onkyo 686 who has 4 or 6 ohms impedance setting. Can I use speakers with different impedance? - Hear and front - ( 4 ohms) - Polk Audio - 5-1/4" Bookshelf Speakers - Center - ( 6 ohms) - Polk Audio - Dual 5.25" 2 way - Sub (6 ohms) - Sony”