This is an old thread, but still a resource. I wanted to do a follow up. The V-caps, particularly the copper foil, Teflon caps are indeed remarkable. The add clarity to the Nth degree. After over ten years with mine, used as coupling capacitors on my EAR 864, I began to realize that my preamp was not gelling with several of my speakers. Namely the JMR Bliss Silvers, and later the Joseph Audio Pulsars.
I could not understand why they both sounded so hot in the upper midrange. Also, guitars sounded thinner, especially rock guitar. Snare drums too.
After much tube rolling and amp rolling, I finally considered changing the coupling capacitors. After some research I settled on Miflex KPCU, a Paper, Oil, Wax and Copper foil capacitor. What I got was a much more balanced frequency response. The low mids were fuller. Tonality was more fleshed out and natural. What wasn't lost were the spatial cues, micro-dynamics and clarity afforded by the V-Cap. It was a massive upgrade.
After the upgrade, I was able to roll tubes with more success. I got the full flavor of the tubes, and I am now reassessing the quality of my preamp. It has gotten quite good. I was thinking about buying a new one.
For perspective on my perspective, I primarily listen to European Jazz and Classical. We are addicted to seeing the Chicago and Milwaukee Symphonies about 15 times a year. I also used to have a recording studio, back in the 90s. I am also a musician for the whole of my adult life (60year old). I have a strong, developed perception of natural sound.
I have also put V-caps in a vintage Eico HF-86, and though I haven't touched that one yet, I do recall a similar thinning of the tone. That will be my next move.
Since this thread was started, there have been a number of innovations in the HiFi capacitors market. I've noticed that Backert is now using the Teflon caps in their power supplies, but oil caps in their signal path. Miflex has had much success, and Jupiter has enjoyed a lot of success with their modern take on a vintage capacitor. Innovation is good for the audio pursuit. I am looking forward to experimenting with several. Maybe my old Audio research VT-60...