I don’t have much experience with subwoofers so my contribution may be worthless. Easy or hard? I suppose the question is closely correlated to expectations? To me, proper integration means the sub blends rather seamlessly with the main speakers and nothing sticks out like a sore thumb. I don’t know, but for a seamless integration the impact of the sub is usually small so as nothing sticks out like a sore thumb. A small but appreciable difference. In my case, I would say easy but as mentioned above, the impact of the sub in my system is not very significant or earth shattering.
I’m still trying to figure out if a superior sub will bring a more significant difference to the system, and whether the integration of the sub will be equally easy or require more effort. I will soon find that out..