Okay, I'll get in on this. Since the OP's question mainly asks about cables (and not equipment), I'll offer - for my brain and ears:
Biggest Impact(!!): RCA analog interconnects. Number one on my list - hands down
Runner up: Speaker cables
Lowest impact (again, for my ears and brain): AC power cables
Since I use a mix of balanced and unbalanced analog interconnects; low capacitance, oxygen free copper and heavy shielding (double braid or Reussen), are qualities I seek out. I would also add ethernet cables as other important cables I pay attention to. There's no question in my mind that upgrading a small 3' ethernet cable added more resolution and detail in/to my streaming experience. It's very possible that since I already pay such close attention to my AC, that further upgrading AC cables just never makes a big difference in my audio system.
Let's also keep in mind that audio is very subjective. Everyone's brain and ears are not the same. High performance audio reproduction (and how to attain it) is a learning experience. Everyone has their own priorities. For me, it's a quiet noise floor, with no external EMI or RFI generated pops and clicks. When critically listening, my main source will always be headphones, and headphones can sometimes be like an audio microscope.