hu crossover vs amp crossover?

My HU has a 12db crossover on all channels. High pass on 4 channels. Low pass on sub out. My amplifier also has 12 db crossovers for speakers and sub (Boston acoustics GTA-1105). i had both the HU and amps crossovers set at same frequency thinking it would be more effective, but i read on another post that doing so, one will cancel the other out and/or maybe create some sort of problem around the crossover point. Is this true? If so, and i should only use or need one of them, do you think the crossover on the amp would be of better quality than the one inside the HU? Or the other way around?

ive never had a problem with having two different crossovers active at the same time but its really not the right thing to do either. one crossover should be defeated and the other set as your main crossover. the quality of the crossover just depends on the price and brand of the amplifier or radio in question. if its a cheap amp then the crossovers are probably garbage too. the biggest plus of an amps crossover is that they are usually fully adjustable as opposed to how a radio has preset crossover points. the radio's crossover has the advantage of being more precise by having set points but it usually will have less range than an amps crossover.