The impedance setting only affects the rail voltage to the internal amps, it shouldn't have done anything to the low level output.

I guess the Yamaha could be sending out a slightly higher voltage than normal which could be affecting the emotiva. Maybe you need to run down to Jason's with the emotiva this weekend and try it out with his Denon.

Jason
M80 v2
VP160 v3
QS8 v2
PB13 Ultra
Denon 3808
Samsung 85" Q70