Well, for one thing, AHCI and IDE operates at different speeds. So if you cables are slightly out of spec, they might work in IDE mode, but fail in AHCI mode.If I'm on IDE and I see no errors (which I have not for the past 2 days) how could the cables be harriewarrie?
But the second point is; it takes you a short time to try other cables (assuming you have them, and the machine is within reach) and even if it isn't the cables then you have checked out one point of possible things from the list.