BTW I do not recommend tampering with the feedback resistor- such things can lead to oscillationThis is why I say get a tech (not yourself) to disconnect the Alps passive, change the gain with the feedback to half of what it is, as he will scope it and compensate for stability.
tenoris OP
And then once that is done you can use your AR preamp which you are so insistent on using, with the volume up around or over 12 o’clock. And this is what you searching for.
Cheers George