Yes, those were the regular Supremes, which I considered a big improvement over the stock Auricaps. I didn't notice the high-frequency emphasis until after I heard the Duelunds in there; they had a much fuller sound, especially in the lower registers.
Tonality is where the CAST caps excel most, in my opinion. Everything just sounds more real and more natural with them in the preamp. The Mundorfs gave a tiny bit more shimmer to a cymbal, but had a small amount of HF glare that the Duelunds don't have; the Duelunds are thus easier to listen to for extended periods - the Mundorfs sometimes gave me ear fatigue after extended listening; so far I have not experienced that with the Duelunds.
Tonality is where the CAST caps excel most, in my opinion. Everything just sounds more real and more natural with them in the preamp. The Mundorfs gave a tiny bit more shimmer to a cymbal, but had a small amount of HF glare that the Duelunds don't have; the Duelunds are thus easier to listen to for extended periods - the Mundorfs sometimes gave me ear fatigue after extended listening; so far I have not experienced that with the Duelunds.