The sensitivity does not affect it being safe or not for the amp. That affects volume of each pair. Higher sensitivity will play louder, but if it's only 1db, you likely will not hear a difference. The impedance is what can present a problem. Playing both pair at the same time would require that both are 8 ohms. This results in a 4 ohm load to the amp. From a little research it looks like the L470 is 8 ohms, but the L620 is a 6 ohm, so the combination is risky. No doubt the amp would get hot.
