Whoops,
I am a little reserved for this project, because my other DIY DI box with just two transistors few resistors and capacitors, and that is almost total proof to get to work, over the years has resulted in thousands of questions and problems.
The Tube DI-box is more difficult to build, partly because it is a "point to point" and that it includes a power supply with stabilized high voltage and rectified filament voltage.
Therefore, I am afraid it will be even more question and problems, and I have no time right now with this.
Me and my company is retiring this year, so maybe a little later in the future I can get involved and have time with this project.
Best from
--Bo--