The Kenwood seems to be a very capable European model. I don't see any reason why it would not work for you.

The Onkyo is rated 125W@6ohms, so you should not be able to perceive any meaningful difference in SPL between the two.

Honestly, I don't think your Yamaha is going to have trouble driving the M80's. If it does, you could shop either one of these amps on price and feel comfortable. But that's just my opinion.

I'll leave the EE's to explain Ohm's law.

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