A well designed amp should not have any problems with 4 ohm nominal impedance speakers IMO. Or at least they didn't in the 70's. Back then even a basic 12 - 25 wpc amp from the likes of Pioneer, Marantz, Realistic and others did a great job with 2 pair or 8 ohm, or one pair of 4 ohm speakers.
I was just listening to my 35 year old 10 wpc Realistic STA-7 receiver with the 4 ohm speakers I've been using for many years and have never had an issue that more current would correct. For the SPL's I normally listen to (80 - 90 db's) there is still enough power to effectively drive a 4 ohm load, even with low sensitivity speakers at -3 db's. Of course it's not as transparent as the better amps, But the bass response and the SPL's I would expect are way better then they have any right to be.
The reason 4 ohm loads stress Some Newer Receivers/Amps is because in order to market them with higher power levels (say 70 wpc vs 50 wpc at 8 ohms), is they must limit the amps current output that they would try to deliver when a 4 ohms load is present. Far worse then just running out of current and clipping, this can cause an amp to become unstable and oscillate, Frying the connected speakers in short order even at power levels far below clipping.
The cheapest way to limit current is simply to restrict the speakers impedance by using only 6 ohm or higher rated speakers, and sometimes by installing a cheater switch, Which reduces the amps output to where it should have been to begin with.
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The back of many amps and receivers tells us all we need to know about minimum speaker impedance. If not check the owners manual or check on line. Just because an amp is rated at 8 ohms it does not mean it won't safely drive a 4 ohm load. With stereo amps/receivers (not 5.1/7.1 AVR's), If it has an A + B speaker option for speakers, Like my 10 wpc Realistic stereo receiver has, Then it is likely stable into a 4 ohm load. If you keep the volume at -3 db's (1/2 power) then you should be fine if the amp is operating correctly.