This is quite some project. Congratulations. I was one of the original 10 beta-testers for Allen. It took us about 2 years to build the RTP-3C. I later bought an RTC-3D from Allen, which was built on PCBs. I have been using my prototype RTP-3C as a platform for experimentation. It is now serving as my tape head preamp after I changed the RIAA EQ to tape EQ. My experimentation with different coupling caps led me to use the Wima FKP4. This is a metallized polypropylene film and foil capacitor, designed for pulse applications. It is completely transparent, uncolored and super fast. I don't believe in using caps to "season" the sound. I just want them to get out of the way. I also changed the series type stepped attenuators to a ladder type with constant input impedance. Allen always warned against using other types of attenuators, because a constant 50k input resistance is needed for the RIAA network. I have found a 48-step attenuator using precision resistors that have a pretty much constant input impedance. At least, it does not make enough of a difference that I can detect. The transistor at the phono input stage cascode has been upgraded to MAT2. The RTP-3D uses a different transistor. The power supply capacitors were electrolytic initially, but now, only metallized polypropylene caps are used. I am also using only Lemo Redel sockets and plugs that Allen favored. Even though I don't have a lot of experience with commercial high end preamps, I must say that the RTP-3C/3D is extremely fast, uncolored, detailed and dynamic.