I would repeat, impedance may or may not be an issue, one must know their listening habit and seating distance. Both could have more effects, i.e. a more important factor than the impedance spec itself.
As an obviously exaggerated example, if you sit 3 meter from your speakers, and listen to no more than 94 dB peak, your little amp may be fine with your so called 4 ohm nominal speaker. If you were to listen to 100 dB peak and sit 4 meters from the same speakers, your little amp will have to deliver almost 4X the current during those peaks, can it do it then, is the question.
Yeah. I sold a KEF R11 + Yamaha RX-A4 to a client in Oklahoma.
People like
@TLS Guy would tell him that unless he uses a separate amp, his speakers and AVR would blow up.
My client was planning on getting an excellent ATI amp, but wasn't ready to buy yet. I told him to just take it easy and slowly increase the volume. Now after about 5 years, he still is just using his lowly Yamaha AVR.
TLS Guy still thinks his speakers and AVR will eventually BLOW UP.
But seriously, like you said - it's about speakers, volume, distance.
I sold another client in OKC with a Yamaha RX-A3080 and DefTech speakers with the built-in sub-amp and high sensitivity. But because his volume is so high and distance far, he had to add an ATI amp.
So it's not just ohms. It's ohms, sensitivity, volume, distance, all of the above.
For some cases, even flagship AVRs won't cut it alone. Not even the Denon X8500 or Yamaha RX-A8 - they had to add amps.
But for some cases, even lower-end AVRs will do just fine.