The manual for the HTR6090( I would think the 6190 is nearly the same ) has a spec:

• Dynamic Power (IHF)8/6/4/2Ω .....................155/195/250/330 W

So I guess it should work with a 4 ohm load but usually a receiver that works at lower resistance will have those specs published more like:

• Minimum RMS Output Power for Front, Center, Surround,
Surround back
20 Hz to 20 kHz, 0.04% THD, 8 Ω .................................... 120 W


Buy the M80s and if the receiver doesn't work out, you now have a great reason to upgrade the AVR

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