I would recommend keeping your ProtoDAC intact. Two options. Build the tube board with a TDA1387 X8 module. Use unshielded jumpers from the RPi using I2S resistors.
The other option would be to jumper from the pin 6 and pin 25 leads of the TX2575s to the tube board. The 420R resistors will be in parallel with the 90 ohm on the tube circuit.
The other option would be to jumper from the pin 6 and pin 25 leads of the TX2575s to the tube board. The 420R resistors will be in parallel with the 90 ohm on the tube circuit.
Hardware: RPi Zero W | Allo Kali | ProtoDAC TDA1387 X8 | PGA2311 | Icepower 500ASP | Harbeth SHL5
Software: Moode 8.3.3
Source: Win 10 NAS
Software: Moode 8.3.3
Source: Win 10 NAS