Using our amplifiers with higher impedance (16 ohm) speakers will be fine. You may find that the overall loudness is slightly lower than if using lower impedance speakers, but this can be addressed simply by turning the volume to a slightly higher position than might normally be selected if using lower impedance speakers. This will not create any problems for the amplifier.
Also, the rated impedance is just an average, so the speakers are unlikely to be at 16 ohms for much of their operation, and may fluctuate above/below this at points in their frequency range.
Low impedance speakers (4 ohm) create much more of a problem for the amp, due to the lower resistance, meaning that more current is drawn and the amp gets very hot.