While the CH silver cable is very dynamic & balances and 'neutralizes' the Quad's fq curve beautifully.. the Quads with the BTG-Audio copper cable seems to maintain a sound closer to the Quad's 'native' sound signature & frequency curve. Plus, it's less microphonic, softer, & more flexible. The silver cable tames the overall bass & tightens the midbass fq's to an impressively linear extent. Heck, it might be too linear for some. Compared to the copper cable.. the silver's bass is tighter and more neutral, the midrange is very dynamic, but note weight is (comparatively) thinner, and the silver's treble is more sparkly & airy.
While I like those aspects, I realized that I missed some of the Quad's 'native' tuning: namely its smooth, slightly laid back character and delicately boosted bass. The copper cable brings those very things back.. while keeping resolution and clarity nearly on par with silver cable. With the copper cable, the bass is still tighter and more linear than with a stock or SPC cable.. but it's got more quantity than compared to the silver cable. The copper's midrange is smoother and slightly more laid back.. notes have a thicker tone than vs the thinner (albeit, more detailed) sound the silver had. While treble with the silver cable had a (comparatively) more airy, energetic presence.. the copper's treble is on the crisper side. It's still very articulate and detailed, the tone is just slightly different. The silver cable boasts a larger soundstage in all directions (while not UM Miracle 'large' in a spatial aspect, it makes use of the space incredibly well.. it's very 3D). The copper's cable tends to image in a more speaker-like fashion & it has better center imaging.
I didn't find the copper cable an 'improvement' over the silver, per se.. more of a sidegrade that presents a slightly different presentation that's more in line with the Quad's smoother overall tone. I see myself using both these cables, actually.. depending on my mood. The silver cable's dynamics and detailing is spectacular, it seems to bring the technical aspects of the Quad out more.. but it might tame the bass too much for some. The copper cable offers a sound that showcases the Quad's native fq curve.. but in a more articulate, cleaner fashion (than the stock Westone or SPC cable).. while offering clarity & detail that's nearly on par with the silver cable.