I can tell you some of the 'higher end' cables I've heard definitely try to provide a more laid back sound and warming things up. Whether alloy choice or adding caps and/or resistors and what not. I personally think it tends to kill the music but others seem to use it as a tone control to mitigate digititus upstream or in the transducer. None of that is measurable in FR wrt alloys btw. Same as why two flat measuring amps could sound bright and analytical or warm and relaxed. Look and measure elsewhere.

I can tell you some of the 'higher end' cables I've heard definitely try to provide a more laid back sound and warming things up. Whether alloy choice or adding caps and/or resistors and what not. I personally think it tends to kill the music but others seem to use it as a tone control to mitigate digititus upstream or in the transducer. None of that is measurable in FR wrt alloys btw. Same as why two flat measuring amps could sound bright and analytical or warm and relaxed. Look and measure elsewhere.

Some cables like Cardas Golden tend to have a very warm signature sound. Others like Nordost or XLO are the opposite, thin and somewhat clinical. I can't point to any measurements on why that would be so. You just have to try them and see.

I know Blue Jeans Cable has an ultrasonic welder... do any of the other "boutique" cable makers have similar capabilities?

Audioquest uses pressure welds. I'm not sure who else does those sorts of terminations.

Having gained technical background and training i try to make better sense of the world but finding myself consistently failing in making sense of technical side of audio depths.
Some things make sense while others just don't, so far, for me.
The engineers who have cracked something great (guys at Schiit, EC etc) apparently have deeper knowledge in the field (not just book knowldege) or have been extremely lucky in trial and error.
  Some book worm objektivist/super atheist types have apparently hard time accepting things beyond common knowledge.