I don't know of any gain that has a setting of "24". The input sensitivity ("gain") is a range of voltages, not a numerical range like a volume setting, and that range is determined by the design of the amplifier. Where the input sensitivity needs set is based on the input voltage of the preamp signal. For example, the range of input sensitivity would be .2V - 8V. The gain would be set somewhere in that range based on the level of the input signal. Anyways, you can set the gain as low as you want. Being too low doesn't hurt anything, you are just not receiving all of the output power capabilities of the amplifier. Getting "close enough" is good enough because under most circumstances you are not going to hear a 25% difference in power (in reality the percentage can be higher, I'm just trying to keep it simple here for you). So if you set the gain too "low" and undershoot power output by 25% you are not going to know because you are not going to hear a difference. As for setting the gain too "high", you are safe for a while. A little clipping isn't going to hurt anything. Clipping is a little worse on speakers than subs because it will probably end up being more audible, but it probably won't hurt anything unless you are already pushing the drivers thermal or mechanical limitations (which is the only time a loudspeaker is damaged). Clipping in and of itself doesn't hurt anything, other than possibly making things sound worse because of the added distortion. A driver, any driver, is only damaged when it's thermal or mechanical limits are exceed. Clipping may be the reason the driver's thermal or mechanical limits are exceeded, as a clipped signal contains more average power over time than a pure sinewave. But it's the increase in power as a result of clipping, not the shape of the waveform or the "clipping" of the signal itself that does the damage. This is why people recommend just setting the gain by ear. Small differences in either direction aren't going to matter. Set the gain a little too low and you won't hear a difference because realistically you need a substantial difference in power to actually hear the difference. Set the gain a little high and the small amount of clipping isn't going to damage anything....with speakers it might sound worse because of the distortion, but generally with subs the clipping won't really be audible. Now obviously you don't want to completely overshoot the gain setting because it is possible to start damaging equipment if you run into heavy clipping and you are exceeding the driver's thermal/mechanical limits. But you need to be really far off and/or running unnecessary bass boost/etc before you reach this territory. If you are absolutely lost, the DMM method is a good place to start and tune the gain from there.