I've never heard the Promitheus, but have made a TVC using Stevens & Billington TX-102's supplied by Bent Audio when they could still be had. Since you ask about
RVC's too, resistor-based passives, let me say that I found my TVC to outperform two RVC's, both using Shallco switches (as does my TVC), one with Holco resistors and one with Audio Note Japan tantalum resistors. Then I made a shunt design RVC using Texas Components TX2352 Vishay resistors, and it competes well (without beating) my RVC. I use low capacitance interconnects, and though they're 9' long I have none of the oft-cited problems with RVC's. Those TX2352 resistors are simply great--I've made huge improvements in three phono preamps by using them as 47K ohms input loading resistors, for example. I hope this info is useful--feel free to email me for more detail.
RVC's too, resistor-based passives, let me say that I found my TVC to outperform two RVC's, both using Shallco switches (as does my TVC), one with Holco resistors and one with Audio Note Japan tantalum resistors. Then I made a shunt design RVC using Texas Components TX2352 Vishay resistors, and it competes well (without beating) my RVC. I use low capacitance interconnects, and though they're 9' long I have none of the oft-cited problems with RVC's. Those TX2352 resistors are simply great--I've made huge improvements in three phono preamps by using them as 47K ohms input loading resistors, for example. I hope this info is useful--feel free to email me for more detail.