Upgraded banana plugs

I recently upgraded my standard gold plated banana plugs with Audioquest Suregrip bfa banana plugs, which are silver plated over copper, to get a better quality connection and to hopefully add a little extension at the frequency extremes. What I ended up with was a totally different sound. I went from a warm, musical sound to a much bigger and brighter, dynamic in your face type of sound. I lost a lot of the tube "magic" afterwards and it was like I replaced my tube amps with a solid state amp type of change in sound. Can anyone explain how changing just the banana plugs changed the sound so much? Is the gold/silver plating more responsible for the change or is it the better grip/design of the plug?

Here is my equipment lineup:

Tekton Lore 2.0 speakers
Cary Sixpac monobloc amplifiers
Audio Research LS15 preamp
Squeezebox Touch > PS Audio Digital Link iii dac
Speaker cables are Belden 89259 (Jon Risch recipe)
Interconnects are Belden 89259 terminated with Eichmann Bullet rca's