A word on cables and psychology... In effect as soon as we make a purchase decision, we WANT our choice to be validated. In subtle instances of perception, we can easily "hear" differences that only exist because we are paying attention. And when we don't make blind comparisons we easily influence our own perceptions by "knowing" which gear is in use.
Unfortunately, A/B testing is really hard to pull off, in part because our "memory" for sound is not so great. It's like looking at a breaking wave on the beach, we see the detail as it's happening, but comparing to the next wave is very difficult as we are really left with points of detail or impressions.
For all these reasons, the "super cable" myth is very easy to propagate, and very hard to prove or disprove. Ultimately, I can really only say this: as an EE I have built a lot of audio gear, and done a lot of testing. Most cables that purport to make a big difference in sound are doing so because they either are filtering out information due to high capacitance or inductance, or are adding some sort of ringing to the transient response. Why? At their heart, all cables are nothing more than a LCR circuit, which means they are acting like a filter or a introduce resonant peaks that reduce signal amplitude and alters the waveform. Oh, by the way, the internal cabling in your electronics and/or phones is probably incredibly cheap stuff...
The ONLY cables I have ever seen which really totally knocked it out of the park by having a real solid engineering approach are those made by Goertz, but they don't do headphones (no, I have no interest in this, but actually did buy them for interconnects and speaker wires at home once I measured their performance). I certainly haven't tested them all, but in most cases there is no reason to.
So, for lay people who aren't engineers what are some tips for cables that should be considered?
1) For low/line level signals, shielding is very important, and shields should be grounded on one end only
2) XLR/balanced cables are also excellent for line level, if you have balanced gear, as it cuts out most RFI and EM interference
3) For speaker/phone level use, well higher gauge can reduce loss due to resistance. Other effects are really going to be pretty subtle, so before you go there seriously get the upstream components optimized, you'll get way more bang from an extra $300 on your DAC/Amp than on a fancy cable.
The 650 is wonderfully detailed and revealing. Since micro-details are easily heard, create the best possible signal, and protect it when it's at it's lowest amplitude with balanced or well shielded interconnects. Buy a fancy amp to phone cable if everything else is nailed and you have $ to spare, but know that your brain may well try to fool you into believing you hear a difference that may not exist. Happens to everyone, me too. It's how we're "wired..."