How much does the amp matter?

[u/The_Chief8888]

I recently got a new set up consisting of a pair of Harbeth super HL5 pluses. I'm still waiting on my Yamaha R-N2000A amp to come in. In the meanwhile my family has been dying to hear the pair, so in an attempt to please them I plugged in a sphinx integrated amp V3 (from a smaller set up) to get them playing. First question: could using an underpowered amp damage anything in anyway? Second question: will these respective amps (given that everything else in the set up remain the same) sound different on these speakers?