No problems at all. Speaker impedance is just a rough value as it varies massively with frequency anyway. The problem will usually be with too low impedance anyway. Higher impedance speakers are an easier load to drive as far as the amplifier is concerned though as the impedance increases, the efficiency goes down. If you have a perfect amplifier and very low impedance speakers, you should get more power. In the real world, as the impedance decreases, there is an initial increase in power output but this rolls off and decreases at about 3-4 ohms for most amplifiers. CX100s will be fine! My LS3/5As are described as 11 ohms and the earlier ones as 15 ohms. Almost any amplifier can drive them!