1.) About the jumpers to configure XLR attenuation (from 0 to -30dB): in the pictures in the manual, the jumpers have this small metal plate behind the pins inside the jumper itself. These all point downwards in the official pictures, but in my PRE P3 and P4 have the plate inside the jumper pointing upwards. Does this affect anything? I corrected the jumpers to look like in the manual picture while I set it to -30 dB. There´s no mention about it in the manual.
No, the orientation of the jumpers doesn't affect anything. They work the same either way. I'm glad you asked this, because it probably deserves a mention in the manual.
2.) I have a CD transport that sends digital via BNC. I have two cables: BNC-BNC and RCA-RCA, both 75 ohm. I also have to adapters: BNC-RCA and RCA-BNC. Which one should I use? Is there any difference? So two options are:
a.) plug in an RCA-BNB adapter into the RCA #3 digital in of the PRE, and then use a BNC-BNC cable between the two units.
b.) plug in an BNC-RCA adapter into the BNC out of my digital transport, and then use my normal RCA-RCA cable between the two units.
Again, either way will produce the same result. If the DAC1 PRE were susceptible to jitter, I might recommend a specific configuration/brand, etc, but the DAC1 PRE is NOT susceptible to jitter, so all you need to worry about is getting the data into the input and let it work its magic (or, as I prefer to say, let it work its science).
Best,
Elias