Hi fish,
And welcome. Old stereo receivers were fairly robust, and since they were only two channels, there usually weren't cooling problems driving a 4-ohm load (more current into a lower impedance equals greater heat from the output transistors) so I expect your Kenwood would certainly drive the M80s to ample sound levels. However, 40 watts isn't much potential power for dynamic peaks on the M80s, which can handle hundreds of watts (tested in excess of 700 clean watts per channel without damage), so you'd have to be careful not to drive the Kenwood into clipping distortion that could potentially burn out the M80 drivers.
By the way, you'll notice a HUGE difference in accuracy and sound quality from the old HPM Pioneers. While those still sound good to you, you've accommodated the sound quality of the Pioneers as your reference, warts and all. Most of those old Japanese-branded speakers were very non-linear and colored, with really wonky frequency response curves when they were measured in an anechoic chamber at Canada's National Research Council back in the old days. At that time, they were no match in double-blind tests with early models from Axiom, PSB, Energy and Paradigm. I can think of only two exceptions in my years as an editor of audio-video magazines.
I think you'll be thrilled with the neutral wide-range sound quality of the M80s compared to the old HPM Pioneers.
Regards,
Alan
