Look at that look at that owner's manual!
https://usa.yamaha.com/files/downlo...b_ZX95350_R-N803_R-N803D_om_URL_EnFrEs_A0.pdf
Yamaha has gotten so cheap that the power supply Strangulation Switch is now implemented in software, as part of the "advanced set-up menu". They can't even provide a hard-wired manual switch. If your speakers are 8-ohm nominal, that's maybe not a problem.
Mine were advertised as 4-ohm, but modifications I've made since then will have reduced the impedance somewhat.
The thing is going to suck into a 4-ohm load. Whether that's due to an undersized power supply, undersized heat sinks, or underengineered output transistors (or some combination) I can't tell you. I
can guarantee that Yamaha cut corners to improve profit margins, and the result is compromised "low"-impedance drive capacity. (To me, a nominal 4-ohm load doesn't really qualify as "low impedance", when 4-ohm nominal impedance has become hugely popular in the speaker world. <2 ohm nominal is "low" impedance.)