I knew someone would try to convert me into his faith.
You're mistaking beliefs with real personal experiences.) If a person says that hearing a difference between opamps is impossible why would I challenge his/her real personal experiences? I've heard such talk about cables before.
I've heard differences between different opamps, especially when used in I/V, LPF and Gain stages. Usually this is happening because some opamps are oscillating and sometimes because they are not 100% compatible with the surrounding circuitry and higher THD or noise may occur.
Like I already said in my above post: between V6 Classic and V6 Vivid there are audible differences (test done with identical equipment in A/B test), but I don't remember seeing different figures in the measurements. Vivid is more bright and full of details, although I remember that freq. response was perfectly flat. I will try to do some measurements with these two opamps, when used in different audio stages of DAC and headamp (I hope this weekend).
I wrote in another post on this forum that MUSES01, when used in I/V of PCM1795 DAC chip, had a way more pleasant and warm sound, with increased soundstage, in an A/B test vs. the same equipment with NE5532 inside. When I measured them with ARTA and RMAA I found out that MUSES01 had an increased THD, especially the first 4-5 harmonics, and I also suspect them of bit of oscillations. Same happened when I used OPA2604 in LPF stage: increased soundstage and mellow & warm sounding, but opamps were heating up like crazy and harmonics got higher and higher every 2-3 minutes (probably because of the opamps getting overheating).
I don't think we should argue about opamps sounding different, because this is true for some audio devices and it's audible in A/B tests and sometimes even measurable. Better, let's find a way to measure these differences, other than freq. response.