Your amplifier should not have a problem with the variations in impedance of your speakers if this 4.3 Ohm is a minimum impedance of an 8 ohm rated speaker.

On the other hand, sound quality will definitely be comprimised, when your volume and musical reproduction frequencies cause the speaker to reach its minimum impedance if both speakers are connected (amp will probably clip at a lower volume level than if you had only one set connected).

This comment does not mean you can abuse the speakers and amp.

If you plan on keeping both speakers on for a few hours at maximum volume, or are having a party, where any fool can crank the volume to max without warning, use only one set of speakers and risk blowing a speaker before injuring your amp. (you should hear a lot of clipping before you cause damage to your speakers or amp)