You have more position flexibility with 2 separate kessil a360x but the lens (oval) orientation of the ap9x are generally better for that type of tank dimension.
Some additional benefits of the ap9x would be that you only have to deal with 1 mounting arm, 1 power supply that is actually way better than the 360x (meanwell), it has no need of a wifi dongle/spectral controller, and it's cheaper to buy 1 + a mounting arm than 2 + 2 arms + 1 controller + k link cable.
Can't speak par comparison though if you're talking about the newer 360XE since I haven't purchased one (yet) and did the numbers yet though but ignoring the that I would pick the ap9x easily.