I don't think you want to change the Yamaha switch to 4ohms, as your reducing its available power. Most AVR's with a 4, 6, or 8 selection switch are best left on 8, at least that is my understading from JohnK and others on this forum.

M80s VP180 4xM22ow 4xM3ic EP600 2xEP350
AnthemAVM60 Outlaw7700 EmoA500 Epson5040UB FluanceRT85