There is no definitive answer. At least you said which amp you were looking into but I'm not going to look at its gain levels, but I will give some info
First What important is your HU preout voltage in relation to your amp input sensitivity. Some amp are 5v - .2v (5v bring the lowest) and my HU for instance is 4v so that will be close to rated power on the amp lowest setting, some people boost signal aswell with EQ's, but there is many setting in HU to back off to actually make less power/preout voltage
But that is all unnecessary IMO. You can safely overpower speaker if your signal is not clipping and a narrow bandwidth, but that's all user preference.
I would run active and open lpf and hpf and use bass blocker (capacitor) to cut frequency for your mid bass and highs you can, now it's possible to distort your signal with a too large of a bandwidth for 1 speaker to play, but you would have to see what your driver is capable of and what you want.
Also the bass blocker info can be found online it needs to work off impedance of the speaker