I definitely fall in to a Category 2.
When transcieving an analogue signal especially, the signal path is susceptible to EMI and RFI. The signal path is subject to degradation and loss along the length.
The longer and thinner a cable, the lower the highest frequency it can reliably carry along its length without loss in signal strength. This coupled with any interference picked up along it's path affects SNR.
SNR (Signal to Noise Ratio) is the difference between the "noise floor" of the signal (The unwanted noise and interference) and the strength of the signal you want to receive. Shielding a cable reduces its susceptibility to EMI / RFI, and lowers its noise floor.
Thickening and shortening the conductors in a cable reduce the losses they incur.
Thickening, shortening, and shielding an interconnect cable increases it's SNR.
Speakers also carry a current concern. I.e., amperage. They draw current. They draw current at low voltages and relatively high amperages. RFI / EMI picked up along the length of a speaker cable are so insignificant they are rarely perceivable by even the most honed ear.
Then we have parasitic capacitance. Also known as capacitive coupling.
What is capacitor? It's two sheets of a conductive material separated with a dielectric. It blocks DC and allows AC.
What's a long, straight speaker wire? It's two lengths of a conductive material separated with a dielectric. Depending on where grounds exist in your setup. running a length of speaker wire parallel to a main cable can result in capacitive coupling and 50Hz hum.
What can we learn from this?
Analogue interconnect cables are susceptible to signal loss, degradation of SNR, and a frequency response curve that depends on the makeup of the cable. Make the analogue interconnect out of thick, shielded copper cable, and keep them as short as possible. That's it. You needn't do any more.
Digital signals are different. A low SNR on a digital cable can result in degradation of signal if there are some serious sources of RFI / EMI but on the whole, much more so than analogue signals, a digital signal either reaches the other end with sufficient SNR to be decoded, or it doesn't. There's no grey area in between.
Optical digital especially.
A different piece of digital interconnect cable can't colour an audio path. It either works, or it doesn't. There's never any character attached to an optical fibre or digital interconnect cable other than that created by the placebo effect in the listeners mind.
Speaker cables - thick copper, not run parallel to mains cables. That's it. A big chonky piece of 10mm Twin & Earth usually used by your friendly sparky to install your power shower will sound no different if used as speaker cable to Nordost Valhalla.
I'd bet a months pay on that on a blindfold test so some audiophiles who aren't told what components are being switched out to identify any difference.